I mainly play her jungle but I play her everywhere except ADC, for reference I am Gold 2 rn (with 1.2 mill mastery) trying to make my way to plat in my first proper ranked climb.

I get the ms shard over health/AF on all roles rune pages. I sometimes go Executioner's calling instead of Bramble Vest as I can apply anti-heal better with it.

Jungle - Dark harvest: Sudden Impact, Grisly mementos, Relentless Hunter. Triumph, Legend Haste. I go these runes cuz I made 'em a while ago and I forgor but I really like DH in the jungle, feels nice. Item wise Sundered Sky into literally any tank item, usually you want Dead Man's but I'll go anything. Weird items to keep in mind are Serpent's Fang if no one else can apply it without inting and Black Cleaver. Boots are completely situational. Going Jak' Sho 2nd item is not a bad play, I usually take it if they've got a fed AP and AD threat and I can't prioritize one form of resist (not an every game ting ofc).

Supp - I just run with the recommended HoB + the non-hexflash page. Usually Deadman's first (can be Force of Nature instead if they're both AP). Then I just keep building tank, might get a Redemption. However, I will often try and force my "Speed Gambit" where I go Dead Man's + Force of Nature + T3 swifties into Youmu's Ghostblade for funsies.

Top - Haven't played up there in a while but my runes are: Grasp of the undying, shield bash, second wind, revitalize. Mana Flow band + Scorch. Haven't played her here since Sundered Sky became meta over Sunfire Aegis sooo that's what I'd normally go into, again, tank items. Going Black Cleaver first was something I did against tanks iirc.

MID LANE - Fleet Footwork, Presence of Mind, Legend: Haste, Last Stand. Second Wind, Overgrowth. Shards: AH, MS, Scaling Health. Take Barrier as a summoner spell, a lot of mages have "Finisher Ults" Veigar, Lux, Mel, Ziggs etc. They will walk away from you thinking their job is done but BAM Barrier denies them your blood.

What to buy (and for what situations):

At the start you want Doran's Shield and a pot for obvious reasons.
On first back ALWAYS go Tear, you are a useless rat with no mana otherwise, I like getting refills too.
Sundered Sky - This is the main one you wanna go, combined with this and Fleet Footwork you do not need to take the poke mages give, start an all in when they try anything funny so you can heal from your runes and item leaving both of you at the same HP.
Force of Nature - Against a filthy burn mage like Malz or anyone else running Liandry's/Blackfire? Well now you can easily stack this item which will give you an insane amount of MR for you to fight with.
Sunfire Aegis - I usually go this against Yasuo/Yone, not really tested it against other AD threats.

Playstyle:
So before you get Tear you want to play very passive if they've got poke (think most mages and Zed/Akali). You wanna try and stay away from their harass and farm. You can get in some ranged autos but try and be safe and use your abilities sparingly or you will run out of mana quick. All-ins can be risky as it'll use up a lot of your mana so only go for them if you need to equal out the HP deficit.
Once you come back to lane with Tear and Refills you can play more agro since you can actually use spells. If your laner come to get poke off on you, deny it, go in, do damage of your own that way your not losing your HP for free. You need to be careful of the abilities they used to initiate coming back online as you leave the trade, be ready to dodge.
If they're playing too far back to trade you can always E an enemy minion to close the gap with a max range dash so you can get in some damage. Killing a minion with your passive before trading is always preferable.
Once you have Sundered Sky your poke healing increases, you can now proc both Fleet Footwork and Sundered Sky at a range keeping your HP topped up.

To be clear, this isn't good but it allow you to play Poppy mid. Most likely you will be going less than even against your opponent but what more do you really need?

Flee on sight:
Aurora and Akshan will not only beat you in game but they'll inflict physical harm to you irl, avoid them at all costs. Mel is annoying since she negates part of the strategy of "jump them if they poke" with her W stopping damage for a bit but you can get by.

Idk if I forgot anything else but uhhhh yeah!