This guide reveals how to build Poppy to become a strong bruiser.

AD marks and quints for last-hitting, and auto-attacking your enemies a lot better.
Defense seals and glyphs to be able to resist both AD and AP champions.

Twenty-one [ad-oriented] offense points to maximize your damage throughout the game, especially during mid and late game phase.
Rest in defense to reduce damage dealt against you.

The items suggested in this guide enable you to:

farm quickly and efficiently [Hydra + Shiv]
stay on enemies [Mallet]
deal substantial damage [Hydra + Shiv + Mallet + Cleaver]
take beatings [Guardian Angel]
resist heavy cc [Treads]

Keep in mind that you're no god walking among-st mere mortals with this build. You still have to play very cautiously.

Q first because it has spammable damage that can also help you cs a tiny bit [don't spam, though].
W second because it gives you some good steroids come mid game.
E last because it's really only meant to either catch up to enemies, or peel them off your carr(y/ies).
R max whenever you can because it's an amazing ult.

Flash because you'd want to be able to either escape over a wall whenever necessary, or get the last-hit/Q on an enemy champion when he/she's low enough.

Ignite because free true damage, healing reduction, and can help you score an early kill if you get your enemy low enough.

This is the best I can come up with to make Poppy viable during S3 because quite frankly, she's not exactly the best and/or most viable pick. Use this guide if you want to clown around in normals or coop vs ai.

I don't recommend picking Poppy in ranked [currently] because there're simply better choices than her at the moment. If you plan on playing seriously and winning your games, then you shouldn't [currently] be picking Poppy unless you plan to troll by making the game a 4.5 vs 5 from champion select. If trolling, then proceed to pick her. Otherwise, pick something better.

PROS:
Damage.
Tanky.
Fun to play.

CONS:
Requires a lot of gold-farming.
Requires skill to play properly.
No reliable cc until you have F. Mallet, and no escapes.