Most prefer top or jg but I love her as a support tank. Peel the adc type playstyle. If your not used to playing a in your face support and are not comfortable with overextending (not too much) and baiting I wouldn't recommend it.
Notes:
-poke with your shield throw, then always pick it up if the enemy jg isn't near.it does great early game damage and picking it back up its difficult for the enemy to get past it in the early game as well unless they have a lockdown support.
-your w grants move speed so don't always feel you need to use it as a wall. A lot of times they may not have many dashes on their team so you can still use the w as a self getaway.
-max your e first. You wanna play protect the adc? then knocking the enemy back more often is important.
-constantly look for opportunities to knock them into a wall for the stun. It is much more effective to wait and use it as a stun than it is as a knockback
-rush dead mans plate after sightstone. As poppy does have the e for engage I think it's better to position it for the stun. In order to position it you need to run at their face quicker. Dead mans does the job whilst apply more tank and cc.
-your e can be the used as an escape on minions and monsters. Think of it as a lesser version of lee sins w.
-your q is a small aoe slow that sits there for a moment. You can use like a very crummy ziggs e. Place it on the ground pointing at them as they are chasing you and if they don't think your q will affect them much they will be slowed and take % of health damage. If they know that the slow is decent it will at least apply zone control as they will run around it. This is kinda difficult to do because it only last about .8 seconds so making use of it as a slow will pretty much just come as you get used to her kit.
-you have a very strong power spike at lvl 3. Burning flash at lvl 3 for positioning for an e stun then pressing q after a basic gives for a lot of damage and if you ping before you goin hopefully the adc will be ready and he can Finnish em quickly for you. It's easier than it seems.
-Poppy is a strong roamer as her intention was to be jg in her rework. Don't be afraid to roam mid after a fight at bot getting your mid fed is just as good as your adc fed.
-many wonder what to use your ult for. Many say double tap it for an instant knockup so your team can catch up to an enemy running away. Basicly your using it as a shitty bard ult then. For me I use it as a finisher if say the enemy is low and thinks he's safe under the turret. But that's rare so more often i use it simply for counterganks. Counterganks. Counterganks counterganks all day. During teamfights if their frontline is in your teams face than use it then to use it as rito intended to turn fights from even to favorable.
-your damage falls off heavily late game as you do not scale well. So relying on your utility in your kit is important. Therefore I reccemend getting at least 20% CDR within your build. It's not to big of a deal however if you implement a 4th item BC as that offers even more utility shredding armor.
-a final build may look like deadmans plate, sightstone, warmogs/righteous glory, spirit visage, black cleaver, locket of iron solari, and any other bruiser item. Feel free to play with it a bit. The core is dead mans warmogs and spirit visage but that's just what's been working for me.
-ancient coin and rejuv beads is a great starting option for her. The ancient coin gives you the most gold and hp whenever a minion dies. Plus some mana regen. It's great because it helps poppy overextend.
-masteries I like the resolve tree more taking bond of stone, legendary guardian, perseverance, runic armor, and recovery for more over extending. Then down half the cunning tree taking bandit, meditation, secret stash, and wander for more sustain plus roaming. Again feel free to change these as you see fit, this is just what works for me.
-for runes all that really matters is move quinns but normal flat marks and the regular armor seals and mr glyphs are effective on her if you need a reccemendation.
That about what I can say for her, I apologize for any misspellings but my brain can't force itself to not oversee mistakes when I proofread.hope this helps