Every opening hand tells a different story, from a different angle, with different characters. Generally speaking you will have some combination of lands, acceleration, resource denial, hate bears, parity breakers, interaction, combo pieces, and equipment. Let's put this another way;
Things you want in your opening hand (In moderation)
1) 1-3 Lands
2) 1-2 of any form of acceleration
3) 1-2 Relevant hate bears or hate pieces
4) 1-2 pieces of resource denial / stax piece
5) Tutors
6) Card advantage
7) Parity-breaking // Interaction
Things you don't want in your opening hand
7) Combo Pieces
8) Equipment (unless its Lightning Greaves and something in your hand is a silver bullet on a creature or a tutor)
Things You Always Have In The Command Zone
9) Card Draw
10) Parity-Breaking (Only when Tana is paired with the correct cards)
Why did I prioritize in such a way? Well, 1 and 2 let us play magic, let alone faster magic. Cards that fall under 2 typically also double as parity breakers for 4. Meanwhile, 3 and 4 function to slow down the game long enough for us to mount irreversible advantage or simply lock the game out. Tutors are the catch all for things not present in our hand but require a casting cost, the vulnerability of being countered, and doesn't beat simply already having the cards we want in our hand.
Card advantage is always nice to have, but we readily have that available in Tymna if we desperately need it, and in terms of casting priority we only want to throw out a Sylvan Library or Dark Confidant earlier than anything else if we are trying to force interaction, or if we want to make a greed play and gamble the odds of our opponents not having a decent enough hand.
As aforementioned, most parity breakers are in our dorks / rocks, but there are a few cards that stand out as obvious power plays. Earthcraft, when run alongside Ruination, Blood Moon, and Magus of the Moon, gives us plenty of reason to go a bit heavier on the basics. Paired with token generation from Tana, the Bloodsower or Bitterblossom, we can expect to generate much more mana than our opponents. Phyrexian Altar is an include for similar reasons (but also serves as a sac outlet when we need it, perhaps we want a card in the yard instead of exile when staring down a Swords to Plowshares, or we need to resolve Chord of Calling but our Gaddock Teeg is still on board).
Keeping in mind this sort of priority of cards when looking at your opening hand should be a decent guide for what to keep, what to mulligan, and your possible lines of play before and after considering opponent's vantage points. Playing the hand and the subsequent game is a matter of experience and practice; but we can certainly discuss some general lines of play here.
The idea of our plays is to create as much virtual card disadvantage for as many of our opponents as possible. In theory, creating and protecting a board state where each card in their hand and their deck has no effect on our ability to win the game, or brings them no closer to winning the game for themselves - makes us the sure victor. In practice, the diversity of our opponents decks, their archetypes, card choices, and our fortune or misfortune dictates that not all our plays effects our opponents the same. An example may be that a well-timed Hushwing Gryff will totally hose the combo turn of an Animars player and perhaps even a while after, but will do absolutely nothing against Jeleva or Zur Doomsday storm. Assuredly, there are plenty of plays that likely hurt the widest range of decks across multiple archetypes (aven mincensor, Leoning Arbiter, Eidolon of Rhetoric, a well-timed Ravages of War with a favorable board state, etc). However, we are not guaranteed to have them when we need them every game. Some or many of them may be removed or countered if we play carelessly, while others require time and set up to be effective and others still only serve to slow and not halt progress.
This means you need to prioritize your pieces on success rate and necessity. Be prepared to play pieces to have them removed, and in a case where such is certain consider timing that play to achieve great efficiency or buy the greatest amount of tempo.
That being said, keep in mind that every hate bear and stax piece has a value to each opponent. Hushwing Gryff is certainly not cared for by the Animar player, but may be priceless to the Jeleva player for as long as that player needs time to find the right cards. In a different light, board wipes and removal can often be staved off for several turns when opponents seek to answer your pieces while still factoring in each other player's capacity to win on following turns. This often means that pieces may typically be answered if and only if the combo player can win on the same turn.
Alternatively, you can anticipate your opponent's interaction in an attempt to have them use it on each other, then play your pieces on the following turn. Don't forget that in some cases, one or more opponent's only or preferred answer to your stax and hate pieces is to turn sideways for combat; which begs the necessity to keep your life total in mind and gauge your ability to extend your creatures accordingly.
No matter how you choose to play it, at some point you should aim to put the heavy hitters onto the board. These heavy hitters may be Contamination, Ravages of War, Blood Moon, Vandalblast, Eidolon of Rhetoric; in general these are the pieces that will either lock the game down or effectively bring you to a highly advantageous point. Different board states, different opponents and different games dictate what constitutes as a closer and what does not (as well as when you should play it).
Playing with Board Wipes in Mind
As far as I'm concerned, Toxic Deluge is the board wipe to keep in mind here. Obviously, most other cards will do the job of ruining your board state sufficiently (including an opponent's own Elesh Norn). Regardless, consider that Wrath of God and Damnation coming in at 4 cmc makes it weak to Gaddock Teeg and vulnerable to early mana denial lines of play. Additionally, wrath effects of the heavier casting cost variety can be difficult to slot in (depending on the archetype), and equally as frail to counterspells as cheaper variants.
There is a noticeable gap between the period in which you cast Tymna and the follow up casting of Tana. This is the preferred space in which we should and can anticipate the toxic deluge being cast. The reasoning is simple, if Tymna is left unchecked we will draw into a slew of creature and non-creature threats and cast them as we see fit (perhaps giving the non-creature pieces priority); which lessens the need for us to ever cast Tana. If a board wipe comes down after the Tymna is cast, then we simply follow up with Tana and use our Saproling tokens to lock down the board via Contamination, Smokestack or generate greater amounts of mana via Earthcraft, Phyrexian Altar, etc (which even opens up the feasibility of recasting Tymna if we like).
Other lines of play in our opening hand may be sufficient enough for us never to have to cast Tymna or Tana, or avoid doing so until much later in the game. This gives us plenty of opportunities to force answers earlier, or lock down the board and roll out of the red carpet for our commanders.
General Tips and Tricks
1) When playing with either Tymna or Tana on board, it may be favorable to proceed directly to combat phase, generate your combat triggered resources; and make a better informed decision on your second main. If your opponents mean to foil your combat phase, best to let them try before doing anything else. Eidolon of Rhetoric on the board also means you want to know exactly how your combat phase went and what came of it before casting your one spell for turn. The exceptions to this are also fairly obvious; main phase 1 top of deck tutor (Sylvan Tutor, Imperial Tutor, Vampiric Tutor, Enlightened Tutor, Worldly Tutor, Sterling Grove) into a Tymna draw trigger is a reasonable line of play. Additionally, if you are testing Combat Celebrant with your kiki-combo, keep in mind you will want those pieces on the battlefield prior to combat.
2) In my experience, Crucible of Worlds is counter or blow up on sight; you may see similar results so play accordingly. Furthermore on the issue, recognize that in many cases we cam set ourselves ahead of a our opponents in anticipation for something like Ravages of War easily without Crucible sticking the board. Using the crucible as counter or removal bait is certainly a fine tactic in this sense. Fairly soon we'll also have access to Ramunap Excatavor which I'll be more than happy to use.
3) Playing against fellow stax players can be tricky, because they come equipped with their own ways of keeping themselves from the harm of their stax effects as well as many of ours. The most common way this is done is via mana rocks. Thankfully, we have plenty of ways to hate on artifacts in the build (and you can feel free to slot in your own to fit your meta). Against Teferi and Brago decks, this is likely where you will want to hurt them. Land destruction and Blood Moon / Contamination effects will slow them down but they may still be able to cast mana rocks or have them in strong presence - meaning they can still produce the colors they need to play magic. Against Brago and Derevi decks, bear in mind that your ability to block creatures in the air is limited to a few creatures (that you may not even want to block with without the protection of a sword). Other decks still will play through stax effects via their creatures - which alone is no issue since we also have the tools to deal with them. Consequently, pressure certainly amounts when we face multiple decks capable of one and the other.
4) Many similar lists don't run Swords of X and Y (or any equipment) - and you shouldn't either if you don't want to. Personally, I have found these pieces of equipment invaluable to my build. Providing protection, card draw, colorless removal, creature recursion, and land untaps is no small benefit. The only caveat is that to use them, you must have a meaningful board presence and the opportunity to play them when they will provide some lasting impact. This may typically translate to slowing down the board, or creating stax hurdles for our opponents to overcome while we advance our board state further towards success. As an extension of this point, do feel free to swap and slot in whatever you feel gives you the competitive edge at your environment.
5) Skyshroud Elf is a HOUSE. H-O-U-S-E. I think this card works really well alongside the likes of Contamination, Blood Moon, Magus of the Moon, etc. I would love to see it in more lists, please test it out and let me know what your thoughts are!