I like to place a die on top of my deck after casting Summoner's Pact to remind myself not to miss the trigger prior to drawing.

Always stack triggers with the most options first so they resolve last. Stack triggers where you have no option last, that way you still have the most options available if your opponent responds to a trigger.

Always hold priority after playing an extra land card, and play those land(s) immediately after to play around removal. On this note, try to play a land without a trigger following Azusa, Lost but Seeking so you can get in both extra lands without your opponent having a chance to respond.

If you mulligan badly game 1, it may be beneficial to just not play lands that give away your deck, if you will probably lose anyway (basically play like you kept a 0 land hand). You'll gain information as to what your opponent is playing and they won't have any information. This of course depends on if your opponent already knows your deck, but it is still worth mentioning. This also applies to your opponent playing a searching effect like Necromentia where you have no hope of recovery. It may be beneficial to just concede in response, so they can't see all of your deck tech.

You'll notice that a lot of my commonly tutored for targets have an easily recognizable unique coloring to the card when the deck is fanned out, making finding them that much faster instead of having to search card by card. For example:

Forest - all of my basics are white-bordered
Valakut, the Molten Pinnacle - the only red expedition frame
Primeval Titan - Time Spiral Remastered old frames (different coloring)
Urza's Saga - look for the Saga frame on the left (any print works)
Amulet of Vigor - only artifact in old frame pre-boarding
etc.

I've also considered using "the List" or similar prints to have the small stamp on the bottom left to help differentiate at a glance some cards that don't have unique frames. However, this only works for one or two cards, since multiple cards with the same stamp would defeat the purpose. You can also use the Modern and old frames in a similar way, since the coloring or frame itself is slightly different.

Currently considering:
Tolaria West - it now has the "Heads I Win, Tails You Lose" print with the stamp bottom left
Vesuva - does have a "The List" print

Amulet of Vigor - one of the cards that makes this deck really shine, eliminating the downside of many of my lands, while also giving my titans +2/0 and haste (plus an extra land!). Multiples of this ramp me really fast, and is a force to be reckoned with.

Summoner's Pact - pretty much 4 more copies of Primeval Titan or whatever creature is needed, but be careful with the upkeep (I like to account for them potentially destroying any of my lands with a Tectonic Edge or the likes)!

Explore / Growth Spiral - The main benefit to Growth Spiral over Explore is if you have any lands that can be used in response to something else, for example Sejiri Steppe for protection of a creature, any bounceland as protection against land removal, or an activated Valakut, the Molten Pinnacle that you can use as removal for your opponent's creatures/planeswalkers. You can also use it for extra information in response to a Simic Growth Chamber trigger, allowing you to bounce a different land, or sneak in the one in your hand to reuse, etc. The extra color restriction can backfire, so it is a slight trade-off.

Expedition Map - this is mainly found with Urza's Saga when you are missing a bounceland or a threat, allowing you to grab Simic Growth Chamber or Tolaria West.

Honorable Mentions

Timeless Lotus - this works as some great color-fixing and ramp all at the same time. It coming into play tapped is actually a benefit for us, since it lets it tap multiple times thanks to stacking Amulet of Vigor triggers.

Bitter Reunion - This helps us to filter through our deck faster, is usable through Blood Moon and also gives our cards haste at the very low cost of 1 mana for all creatures. It has a lot going for it although it is a bit slower of a card.

Scapeshift - capable of winning games with Dryad of the Ilysian Grove or Amulet of Vigor + 6 lands out by finding Valakut, the Molten Pinnacle or setting up a (usually) game winning Cultivator Colossus by finding Bouncelands + Tolaria West. With only 5 lands and Amulet of Vigor out, you can run away with the game by transmuting into Primeval Titan in pretty much the same way, depending on which lands you have to sacrifice. With 2+ Amulet of Vigor you only need 3 lands to sacrifice to produce enough mana to transmute into a threat.

It can also function as mana-fixing or ramp depending on the situation as well. Not really the greatest thing in multiples, since most of our lands are important utility lands, but definitely a lot of synergy with the deck overall. It generally ends up a cheaper Cultivator Colossus or Primeval Titan, but sometimes one of your lands in play were important, so it's not always game winning on the spot (you can mitigate this by running both Hanweir Battlements  + Slayers' Stronghold). It's also pretty horrible without Dryad of the Ilysian Grove or Amulet of Vigor, so it isn't ideal against decks with interaction.

Bring to Light - tutor for any 3 drop or lower creature, or even Scapeshift to tutor into a threat with Tolaria West. It essentially works as Eladamri's Call where you put the card into play, but instead of finding something larger than 3 CMC, we find Scapeshift instead. Without Amulet of Vigor for the Scapeshift line, we will look for an extra land creature like Dryad of the Ilysian Grove, a silver bullet sideboard card, Fae of Wishes to cast as an adventure to find the perfect card, or Valki, God of Lies  / Selfless Glyphweaver  to play as Tibalt, Cosmic Impostor  / Deadly Vanity  for value plays. Extra turn cards like Savor the Moment / Time Warp are worth mentioning as potential targets as well.

Fae of Wishes / Wish / Glittering Wish / Karn, the Great Creator - even though Fae of Wishes is technically a creature, it's adventure mode is a non-creature spell, which is what we are interested in mainly. This is the most relevant of the wish cards, since we can still cast it for the adventure mode when hidden away, and it has extra synergy when hit with Turntimber Symbiosis  for a 4/7 flier. Wish is just the most flexible wishing card, letting you grab literally anything. However, it forces you to use it the same turn, so it isn't as ideal as some other wish options in certain scenarios. Glittering Wish is a tutor for anything multicolored in the sideboard. Karn, the Great Creator is the artifact wish and potentially usable multiple turns.

Manamorphose - color-fixing where the main downside is not knowing what card it "really is" when considering your hand for a mulligan. It also doubles as a pseudo-answer for Blood Moon as a happy coincidence.

Eladamri's Call / Time of Need - Even though this isn't quite as good as Summoner's Pact in most situations, they are solid tutors. Eladamri's Call lets you tutor for any creature, which is often the missing piece in the puzzle (solid turn 2 if manabase supports it). Time of Need does basically the same, but only finds legendary creatures. Azusa, Lost but Seeking is the obvious ramp choice, which fits into the deck perfectly, but the Legendary threat can be a trickier card to slot in. Amongst some of the top options are: Elesh Norn, Mother of Machines, The Gitrog Monster, Titania, Protector of Argoth, Dragonlord Dromoka, Atraxa, Grand Unifier, Emrakul, the Promised End, Kenrith, the Returned King, and Golos, Tireless Pilgrim.

Warping Wail - this card has a lot of mediocre uses, but we can run it mainly because it's last mode allows it to be a blocker or temporary ramp while holding up interaction. Being able to counter a sorcery is relevant in some matches, like Indomitable Creativity where we don't really have interaction otherwise. There's also a lot of troublesome creatures that can get hit by the first mode as well, so overall a decent card. It is not be as good as Sakura-Tribe Elder when the other two modes are not relevant, so kind of a trade-off.

Primeval Titan - the main creature this deck revolves around, quite the force to be reckoned with. It often comes out as a 8/6 haste trample vigilance, after fetching Boros Garrison and Slayers' Stronghold with at least 1 Amulet of Vigor out (each multiple means it gets another +2/0). Also, even if it gets removed, you get the land triggers, so sometimes playing into removal is the correct play, and ignoring haste.

Altered Ego - with the increased access to 2 copies of Amulet of Vigor, this is a very powerful option, essentially lowering the mana threshold for 2+ Primeval Titans. You can now play that second titan after transmuting Tolaria West if you have access to 7 mana, with 6 of it coming from the Simic Growth Chamber + Tolaria West you found.

Arboreal Grazer - This is actually fetchable ramp in a sense, because it can net you 1+ extra mana in a lot of situations with a Summoner's Pact (not a suggested path against interaction). It also has reach and makes a decent blocker afterwards.

Azusa, Lost but Seeking / Dryad of the Ilysian Grove / Wayward Swordtooth - Azusa, Lost but Seeking is two additional land drops per turn, which enables Primeval Titan the turn after pacting and having 0 open mana with an amulet and bounceland. However, she is legendary, so you never want more than 1, which is why I generally run less than 4 copies of her. Dryad of the Ilysian Grove is an additional land drop every turn, mana-fixing, and a solid 2/4 body for 3 mana. It also combos with Valakut, the Molten Pinnacle as a win-condition. Wayward Swordtooth is resilient to red removal due to its high toughness. Its high power can also help with Mosswort Bridge even if it can't attack or block. Definitely the weakest of the three in most situations, but it does have its niche scenarios.

Honorable Mentions

Cultivator Colossus - This is basically Primeval Titan's big brother when your hand is mana flooded or a utility land you need is in your hand instead of your deck. It doesn't quite go infinite with bouncelands since you need to fully resolve Cultivator Colossus's ability before resolving anything else, but it is definitely a way of making the most of mana-flooding, letting you draw into things to spend that mana on. This is significantly worse than Primeval Titan if you don't have at least 2 lands in hand. If you have 4+ lands in hand, I would say it is generally better (you can still whiff). With 3 lands in hand, they are generally equivalent, with certain boardstates preferring one option over the other.

Tyrranax Rex - keyword soup, toxic edition... Seriously though, this card fits fairly well by being a near impossible to deal with threat against any kind of control variant. It also helps with any kind of "infinite" life shenanigans, since we can now win through poison counters instead.

Kogla and Yidaro - This fits quite well into the bulky trample and hasty creature theme. It allows a form of creature removal, or an answer to troublesome artifacts and enchantments in a pinch as well. It is a quite versatile inclusion that can swing the tide of a game if used correctly.

Elvish Reclaimer - Surprisingly, this versatile guy is really good at just about everything. It can act as a psuedo-extra land card, a land tutor, a sizable threat to stabilize when you have nothing. This is a 1 drop that scales up as the game goes on, and can also be used as a tutor for the land you really need (really good at finding your missing bounceland or Urza's Saga). You can also use the activated ability in response to the triggered ability of Urza's Saga's 3rd chapter to basically replace/upgrade your land in addition to searching for your artifact of choice.

Gwenna, Eyes of Gaea - This is a very interesting option for the deck, which has some pros and cons to it. The first (and really only) major con is that this card doesn't do much the turn it is played, unlike most of our other ramp options. However, this is a card that can color-fix, and gets us to a turn 4 titan on its own. It also makes it far easier to chain Tolaria West into multiple Primeval Titans since it untaps when playing a 5+ power creature, essentially reducing the casting cost by 2.

Eldrazi Displacer - This card is capable of a lot more than you think at first glance. Its activated ability is where we are interested, which is flexible, because it can be used on both our creatures, and our opponents creatures. Also, since we have Amulet of Vigor this can also act as a psuedo-vigilance for us, while tapping down our opponent's creatures. It is usually best served when activated on one of our creatures with an ETB trigger, but there's other combat trick / protection usages as well. Of note, you can blink your titan, finding to loop for deck thinning, basically guaranteeing a hit with Mosswort Bridge later (start with Crumbling Vestige + Valakut, the Molten Pinnacle if you have Dryad of the Ilysian Grove to sneak in some extra damage). You can also use it similarly to refill your hand, or even find protection like Sejiri Steppe or some other utility land at instant speed. This can enable a lot, while also essentially being a double blocker on its own, so it isn't strictly a combo piece. It is also capable of ramping with multiple Amulet of Vigor or drawing loads of cards with Cultivator Colossus.

Omnath, Locus of Creation / Soul of Windgrace - if you can somehow support the greedy casting cost in here, both are potentially worthy of inclusion. Omnath, Locus of Creation is one of the best landfall creatures ever created, and Soul of Windgrace can be seen as a creature version of a planeswalker, for all intents and purposes. I tried them for a while, but found if I could get to their manacosts, I could get to almost as easily, so I found there's generally better options by the time we have access to the casting cost.

Tireless Tracker / Courser of Kruphix - Tireless Tracker is a form of card advantage that is capable of growing itself, although at the cost of investing further mana. Courser of Kruphix is good at letting me eliminate land draws, which can really be a problem sometimes. It also is Lightning Bolt proof, which can be huge sometimes. Lifegain from lands hitting play is just icing on the cake. Something that is also very relevant for both is that the 2+ power can be just what's needed for that Mosswort Bridge activation.

Elvish Rejuvenator - this is a way to find that missing land that you need (usually a bounce).

Woodland Bellower - pretty decent option with the variety of 3 CMC and below creatures that are viable in this deck. We are still missing enough powerful options to make this guy + whatever comparable enough to Primeval Titan to be a real choice (mainly because this doesn't come down swinging without suboptimal cards), but it is definitely something worth considering as more green creatures are printed. Some better targets are things like Knight of the Reliquary, Renegade Rallier, Kitchen Finks, Rubblebelt Rioters along with all the various enchantment/artifact hate options.

Tolaria West / Turntimber, Serpentine Wood  / Port of Karfell / Littjara Mirrorlake - Tolaria West can transmute into another Summoner's Pact for whichever creature fits your situation best. It can also become any land, a Chalice of the Void or Engineered Explosives if either is in the deck (or any other 0 CMC sideboard card). Turntimber, Serpentine Wood  is basically a land that doubles as a threat with any bounceland later in the game. It is very comparable to Tolaria West in functionality, except it cannot be fetched by Primeval Titan and is a much preferred untapped green source when needed (notable when trying to stretch your manabase a little too much). Port of Karfell is basically recursion of a titan that's uncounterable in most situations and Littjara Mirrorlake lets you clone a copy, great for cheating in another attacker with 2+ amulets.

Valakut, the Molten Pinnacle - this is actually a win-con with enough land drops and Dryad of the Ilysian Grove. Due to the Bouncelands being able to bounce themselves, you are generally able to utilize all your extra land drops on each turn, so this damage can add up really quickly. It can be used to clear the board or to do direct damage.

Vesuva - this is essentially a mandatory include because of all the great plays it enables. Vesuva is probably the best land in the deck, as it can be pretty much anything. In addition to copying anything (opponent's lands included), you can play it untapped copying nothing with Dryad of the Ilysian Grove out to produce mana, an often overlooked line of play.

Boseiju, Who Endures - One of the best utility lands for the deck, since we can easily bounce it back to hand, making it fetchable removal for artifacts, enchantments, and even troublesome lands (essentially a broader version of Ghost Quarter if you don't plan to use it on yourself). It does technically ramp your opponent in most cases, but that's a fair tradeoff for eliminating a more troublesome permanent.

Cavern of Souls - good for control matches, and it can also be useful for colored mana when trying to hard cast more color intensive creatures like Sigarda, Host of Herons. Since we have a lot of bouncelands in here, we can change the creature type named almost as often as wanted, so this is almost like an Ancient Ziggurat that can tap for colorless when not casting creature spells.

Slayers' Stronghold / Hanweir Battlements  - some of the best utility lands for this deck. It allows your titans to come out with haste, you can't really ask for more. Slayers' Stronghold is the better of the two, since it gives haste/vigilance and +2/0, which can be important with enabling Mosswort Bridge triggers. Having both as an option gives you a lot of flexibility in your plays, and makes us less susceptible to things like Surgical Extraction or drawing into our only haste enabling land before playing the titan. Be careful not to overcommit to non-green lands though, as you need green lands for the deck to function early. I generally suggest choosing at most 2 between these and Sunhome, Fortress of the Legion as you don't want colorless sources as much.

Sunhome, Fortress of the Legion / Sejiri Steppe / Mosswort Bridge - Sunhome, Fortress of the Legion is great to block something with deathtouch (take that Wurmcoil Engine - I live and you don't even gain life), or just double your damage. However, Sejiri Steppe accomplishes one of the main goals of this utility slot, which is to help your Primeval Titan live after attacking (against most decks), but it requires no investment of to activate. This slot is unneeded in some matches, so it can easily be sided out when it's not that relevant. Sejiri Steppe + Mosswort Bridge cover the defensive and offensive purposes of Sunhome, Fortress of the Legion in almost every situation, without the need of as much mana investment, even allowing more aggresive plays sometimes, all while being colored mana sources instead of colorless. Mosswort Bridge is the most powerful digging tool and virtual advantage this deck has to offer. Cast off anything for 1 green? Yes please! Need to find some removal because they are just stalling with something stupid and annoying? Keep copying/bouncing this until you find what you are looking for. If you are running Mosswort Bridge, it is basically required to run Slayers' Stronghold + Boros Garrison alongside it, allowing you to get to 10+ power far more consistently. Because of those mandatory inclusions, Sunhome, Fortress of the Legion is a basically equivalent option as well, being in the same colors. Also worth mentioning is that you can use the hideaway of Mosswort Bridge to exile cards you don't want to draw, if you don't plan on activating it prior to bouncing it back to your hand. After a shuffling effect, this deck-thinning helps increase your odds of hitting cards you do want by a few percentage points.

Castle Garenbrig - this is decent as potential ramp if you run enough fetches + Forest Subtypes that it can consistently come out untapped. Not really worth forcing into the deck, but it can be viewed as +2 for mana calculations in a lot of scenarios, so definitely a solid include if there's enough space and support for it.

Urza's Saga / The Mycosynth Gardens - These are super powerful in game 1, but they are also super vulnerable to removal/hate (you basically concede against an early Blood Moon, Magus of the Moon, or Force of Vigor). However, one thing they both do well is allow for a double amulet more often (making them a solid turn 1/2 land). One additional upside the Saga does have going for it is the negatives aren't really preyed upon until games 2/3 of the match making it a powerful game 1 tool, which is why most decks want 4 copies, then side them out as needed. The Mycosynth Gardens needs a first Amulet of Vigor to copy, but it can have us go +1 the same turn, instead of needing to wait. It is a little less vulnerable to hate than its counterpart, since it isn't a Saga or Enchantment, but a little less powerful overall. When comparing the two, Urza's Saga is an investment of 2 turns for an Amulet of Vigor, while The Mycosynth Gardens is an investment of 2 mana, which also requires a first copy for us to copy. While it is pretty clear which of these effects is more powerful, both cards enable us to have an explosive turn 3 more consistently. These are also both colorless lands, which is something you need to be careful of running too many copies of, especially if you have a lot of early plays that want colored mana.

Forest / Snow-Covered Forest - basic lands are needed, enough said. It stops Path to Exile-type effects from being as devastating, and gives hope against Blood Moon. I typically like to use white bordered basics to make fetching easier (you can fan out your deck instead of going card by card) if going with fetchlands, just a little trick I like to use to help speed up games.

Selesnya Sanctuary / Golgari Rot Farm / Simic Growth Chamber / Gruul Turf - green bouncelands, the main thing this deck revolves around. It is a good idea to keep one of these in hand at all times (or a Vesuva to copy one) to make the most of your multiple land drop potential. The only time I play my last one in hand is if it means I can hard cast a bomb that I feel will get through when I untap next turn. Otherwise it is best to keep one in hand with the potential of drawing extra land cards, allowing you to "go off" in a lot of cases (considering you have either an amulet in play, or dryad/azusa in hand, and are just waiting on the other piece).

Honorable Mentions

Crumbling Vestige - You can produce mana without an Amulet of Vigor out off a Primeval Titan fetch. You can also go +1 land with Crumbling Vestige + Slayers' Stronghold instead of Boros Garrison + Slayers' Stronghold when you have Dryad of the Ilysian Grove out, and sometimes that one land can be the difference that enables more burn damage with Valakut, the Molten Pinnacle.

Verdant Catacombs / Overgrown Tomb / Zagoth Triome - Fetches / Shocks / Triomes just enable better mana fixing, landfall triggers, and deckthinning. The triomes can also become card draw when bounced if needed. You should generally pick 5 color lands or fetches, it's a little hard to support both. I generally go with fetches alongside at least one shock, because you still have all the untapped potential, but can choose for them to be tapped sources as well, to make the most of multiple Amulet of Vigor lines.

Aether Hub / Gemstone Mine / Tendo Ice Bridge / City of Brass / Mana Confluence / Vivid Grove / Nurturing Peatland / Yavimaya, Cradle of Growth / Reflecting Pool / Twilight Mire - Gemstone Mine is probably the best of the rest, since you can use it twice then bounce it to reset its counters. Aether Hub is a strictly better version of Tendo Ice Bridge and is next in line, since you can bounce it and replay it without using the to stack multiples for later. City of Brass deals 1 damage whenever tapped and Mana Confluence allows you to pay 1 life for any colored mana, which are very important distinctions, and here's why: City of Brass will deal damage to you no matter if you have a replacement effect on it or not, so things like Yavimaya, Cradle of Growth or Dryad of the Ilysian Grove don't help you. However, since it is damage, and not loss of life, it doesn't conflict with Elderscale Wurm or Worship. Mana Confluence is the complete opposite, so if you use it's mana ability with Elderscale Wurm out and go under 7 life, his ability doesn't prevent it, and you are basically vulnerable again. Vivid Grove comes into play tapped, essentially making it the worst of the bunch as it can sometimes takes away strong turn 1 potential. The draw-land cycle of cards like Nurturing Peatland is one land that actually isn't terrible to draw when mana-flooded. Yavimaya, Cradle of Growth gives all lands the ability to tap for which allows the deck to stretch it's manabase a little thinner. The filter cycle like Twilight Mire helps manafix if you have a lot of non-green double cost cards. Reflecting Pool is basically a psuedo-5-color land that makes cards with multiple of the same color cost a lot easier to cast. It gets exponentially better with more multicolored lands, and is quite nice in greedy manabases like this one.

Lair of the Hydra / Oran-Rief, the Vastwood / Turntimber Grove - Lair of the Hydra is a green land that is untapped when you need it early, so basically another Forest. However, this is a manland, which can let you pump your total power on a titan fetch, or become a threat on its own. Oran-Rief, the Vastwood is great with the prevalence of Unholy Heat in the meta, being able to protect a Primeval Titan by just leaving it untapped, or just pumping creatures, sometimes enough for a Mosswort Bridge activation. Similarly, Turntimber Grove works pretty much the same, but it is better on the titan fetch (being able to pump and tap for ), but is not reusable every turn without other support.

Lotus Field / Flagstones of Trokair - Typically these two lands are a package deal, as they are a nice fetch-combo when you need lots of mana. These are capable of producing 5 mana per Amulet of Vigor and still netting you +2 lands for your Valakut, the Molten Pinnacle triggers when fetched. Lotus Field is also capable of pumping our Elvish Reclaimer on its own (can be used after blocking). Flagstones of Trokair being a non-green source, and Lotus Field decimating your land count on their own are substantial downsides to consider, so you need enough synergy to justify inclusion of these. You'll often see these alongside Elvish Reclaimer due to the great synergy.

Crystal Grotto / Temple of Plenty / halimar depths(wwk) - scry lands. If there's not a whole lot of early plays that need a turn 1 untapped land in your 75, the scry outweighs the slower land in most cases. Crystal Grotto is Zhalfirin Void 2.0, which can let you mana-fix as well, now giving you a relevant untapped version of the temples. Halimar Depthsis similar in functionality.

Ghost Quarter / Field of Ruin - land destruction that can double as another copy of a Forest if facing hate like Blood Moon. It's worth mentioning - don't hesitate to blow up your own lands with Ghost Quarter for landfall or The Gitrog Monster triggers - this has saved me on numerous occasions. It is actually a 3 mana land when fetched by Primeval Titan with Lotus Cobra or Tireless Provisioner out (two landfalls + green). It also allows you to draw 2 cards with The Gitrog Monster (one on the sacrifice cost, then one on the land destruction). In most cases, Boseiju, Who Endures is superior due to the added flexibility, but these are still solid options worth mentioning, especially if you have a way to recur lands from your graveyard. Ghost Quarter is especially good against something that lets you play lands from the graveyard, completely decimating your opponent's access to splash colors.

Khalni Garden / Radiant Fountain / Kabira Crossroads / Blossoming Sands cycle - chump blocker or lifegain slot. Sometimes that is enough to turn the tide of battle, so it isn't to be under-estimated as a utility option. I generally go with Khalni Garden / Kabira Crossroads if I have enough space (can potentially filter the with Wooded Bastion).

Blast Zone - This is more of a utility land to deal with the decks that pump out tons of low cost creatures/board presence. This is basically an Engineered Explosives attached to a land. It's biggest drawback is that it can't hit 0 cost permanents, since it enters with 1 counter on it already. You can also use it to blow up some big hard to remove threat with hexproof/shroud if you have enough mana.

Arena / Quicksand / Eiganjo, Seat of the Empire - targeted removal with their own respective pros and cons. Notably, Arena + Sejiri Steppe have decent synergy as a Primeval Titan fetch package. However, Arena not producing its own mana is the main thing holding it back, so you should consider it as more of a fetchable creature removal than a land if trying to fit it in. Quicksand is probably my favorite of the bunch.

It's important to be realistic about the deck, and realize what the weakest/most unneeded cards are. I'll point out what I consider the top 3 weakest main/sideboard cards, and why I don't think they are "ideal." Feel free to discuss other options or suggest replacements to try out. Right now, I would say the deck feels like it sometimes wants access to more threats and ways to pay for them earlier, but don't all decks want that?

Elvish Reclaimer - this is a very versatile creature, but having a tap ability makes it a little slow. That being said, it accomplishes the blocker criteria of Arboreal Grazer in a more meaningful way, and is an upgraded Expedition Map the turn after it comes into play, putting the land directly into play. Running this shifts the deck towards more of a midrange feel at the cost of some minor explosiveness, so there is a bit of a trade-off.

Castle Garenbrig - this is good for trying to get us to 6 mana naturally, but it is a tapped source without already having a Forest, so not particularly good as a turn 1 land. Because of that, we need to weigh it against our other tapped lands, as we don't want to play too many of them total.

Phyrexian Metamorph - as a copy creature, this is reliant on having something else worth copying. It is capable of copying an Amulet of Vigor as well, which is something worth noting. Other common targets include our opponent's Fury / Archon of Cruelty or other similar payoff creatures.

Replacement Options:
Sunhome, Fortress of the Legion - most lists typically run this to help ensure an easy victory with double Amulet of Vigor and no blockers. I find it a little unnecessary, as you will often win the next turn regardless if that is your board state, and Altered Ego wins in a solid percentage of the scenarios that Sunhome, Fortress of the Legion would, while enabling some it wouldn’t.

Increased copies of anything we don’t already run 4 of, like Arboreal Grazer, Explore, or any key lands.

Sideboard

Forest - this is probably a strange card to see in a sideboard, but it is needed due to our extreme greed. Since both Blood Moon and Magus of the Moon are normally sideboard cards, I had the crazy idea to be greedy game one and compensate with basics game two. This generally allows us a stronger game 1, with minimal downside games 2/3. Since we are generally siding out all of our Urza's Saga against a Blood Moon effect we want a decent amount of untapped lands in the sideboard. What better to side in against Blood Moon then a normal basic. You could have some other untapped lands for this slot, but the density of basics really helps to cripple Blood Moon.

The Filigree Sylex / Ratchet Bomb - slightly less explosive than Engineered Explosives and unable to to be tutored for, there's arguments against running this over a second copy. However, since the primary purpose is 0 or 1 CMC, the ability to not hold up 2 mana every turn is not to be discounted. Two copies of this slot isn't particularly needed either, so there's also that. I prefer the sylex since I can do full art to make searching for amulets easier, keeping them as the only artifact frames for the most part.

Swan Song / Test of Talents - these are both fairly narrow options and cannot be tutored for, so they are by far one some of our weakest sideboard options. I'm currently trying them out as a way to improve my matchups with non-interactive combo decks, where it was previously just a race (looking at you creativity). Both coincidentally line up well against basically every graveyard deck, so I almost view these as extra gravehate cards that hit more decks (running less copies of Endurance actually protects it against mill, so these line up with my strategy).

Replacement Options:
Kozilek, Butcher of Truth / Gaea's Blessing - strictly in there for the mill matchup, which is a really tough matchup otherwise. If your meta doesn't have a lot of mill decks, there's probably better options for this slot. Kozilek, Butcher of Truth is slightly better against Tasha's Hideous Laughter while Gaea's Blessing is generally better if you happen to draw into it, potentially recycling something you need. I've gone with the lower cost Kozilek, Butcher of Truth of the 3 Eldrazi Titans, since it is actually castable if drawn into in some cases, and drawing 4 is a pretty back breaking effect if the game has gone on long enough to get to 10 mana.

Tireless Tracker - Really solid against discard, since we can get in early for card advantage, and this is a must answer, growing threat against any control decks. We are already fairly favorable against most blue decks thanks to Cavern of Souls and Tyrranax Rex so this one's main use is continuous card advantage against discard.

To make things a little easier, I marked all the cards I sometimes side out in various matches with the tag #flexslot if you look at custom categories.

First of all, when heading into game two, I usually decide what to side out first. I evaluate which cards are less than optimal. Arboreal Grazer gets cut to 1 copy against decks that don't plan to attack much. Things along those lines, where you take out suboptimal cards. Something like Fae of Wishes will almost always go out after the first game, since we are moving most of its relevant targets in (sometimes a flying blocker can be useful).

After all that, I decide which sideboard cards could prove useful in the match, and move them in. Afterwards, I adjust to make my sideboard as close to 15 cards as I can, whether I need to remove more "filler" slots like Summoner's Pact / Eladamri's Call, or if I have to move in some of the "better" cards I tried to side out (dependent on the match).

Another option is removing some utility lands that don't really serve a purpose in the match (Cavern of Souls and Sejiri Steppe) depending on the deck you are facing. I generally don't suggest going down below 28 lands with the deck. Also worth mentioning is don't stress about getting exactly 60/15; there's times I will play with a 61 card deck in game 2 (usually against some weird homebrew where I want more options and lots of our sideboard seems relevant).

Lastly, you can always include some sneaky tech like Hokori, Dust Drinker / Worship / Elderscale Wurm if you have the space (I ran Elderscale Wurm mainboard for a while before modern became a removal heavy format). If you're facing anything with a more aggro build, Hokori, Dust Drinker isn't the best option. For example, puresteel decks can be seen as a combo deck, but they are a more aggro combo deck, where they get early board presence. Hokori, Dust Drinker is not a good option against decks like these, since they can still keep applying pressure even without mana with a quick start, and since a large majority of the meta falls into this aggro-esque category, Hokori, Dust Drinker isn't really poised as a solid sideboard option currently. However, the surprise factor of an obscure card like this definitely pays off sometimes, so that's just something to keep in mind. I am talking about obscure cards in general being a solid enough option if you have the extra slots, and am just using Hokori, Dust Drinker as an example. If you feel they will do enough in your meta to justify inclusion, feel free to experiment a little.

I'll add once the 75 is more stable

Tutor for any 0 CMC
Tolaria West + Simic Growth Chamber

Removal
Boseiju, Who Endures + Bounceland

Creature Removal
Arena + Lotus Field
Arena + Sejiri Steppe

Reusable Protection/Unblockable with Sakura-Tribe Scout
Sejiri Steppe + Bounceland

Extra Burn damage with Dryad of the Ilysian Grove and at least 4 lands out
Valakut, the Molten Pinnacle + Hanweir Battlements  for haste (Vesuva can't copy a land entering at the same time, so fetch it after attacking along with the 2nd Valakut, the Molten Pinnacle for 3 copies). You can also target yourself with Ghost Quarter for an extra landfall trigger.

+2/0 and Haste/Vigilance (another fetch after attack)
Slayers' Stronghold + Boros Garrison

Free Plays with 10 power (if you have extra landdrops left, it gets really broken)
Mosswort Bridge + Bounceland - you can stack triggers so you can resolve and activate the hideaway before bouncing Mosswort Bridge back to your hand

Haste without Amulet
Hanweir Battlements  + Crumbling Vestige or a Bounceland and extra land plays to replay the Hanweir Battlements  and give the titan haste

Simic Growth Chamber + Tolaria West - Tolaria West + Simic Growth Chamber lets you transmute into a 0 CMC card
Boseiju, Who Endures + Selesnya Sanctuary - Boseiju, Who Endures + any bounceland lets you have removal for any artifact/enchantment/land
Dryad of the Ilysian Grove + Valakut, the Molten Pinnacle - Valakut, the Molten Pinnacle + Dryad of the Ilysian Grove allows everything to be mountains, so Valakut, the Molten Pinnacle + Hanweir Battlements  becomes one of the better fetch options