Intro
Poppy is a great character. With this build there isn't really ever a point in the game in which you are super vulnerable. Her Q can ruin almost any enemy, her W allows for increased Survivability, Damage Output, and Move Speed, all of which have great uses through the course of a standard game. Her E is simply amazing if used right and is a breeze to line up if you follow this guide, and her R is a very versatile skill that can help you with getting away, tower diving, plain survivability, and even conquering fights that most champions would die in. This does NOT mean she is a tank. She has some tanky attributes, but is a tough and survivable DPS, that's all she is. That being said, here is the actual guide.

Pros/Cons
Pros

Heavy Damage Output
Amazing tower diving Capability
Stun

Cons

Squishy after level 1
Little Damage output early game
No AoE skills

So start off with Doran's Shield, i hear a lot about how you shouldn't start with Doran's items but it provides everything you need for a solid start. Now the shoes you can go with anything but a huge problem i face with Poppy is chasing, even with use of Paragon of Demacia it can be hard. If you are being killed or almost killed by someone dealing a lot of physical feel free to buy Ninja Tabi or if they are a heavy caster or a team with too much crowd control, buy Mercury Treads. Now the build gets fun, buy Sheen, by now you'll have enough mana to get good use with it too. Probably an overused but effective combo is Heroic Charge then Devastating Blow. Wriggle's Lantern is a great item, it gives Attack Damage (much needed), Life Steal, and it eliminate the need for you to buy Wards. Madred's Bloodrazors will boost that oh so important DPS. Hextech Gunblade provides survivability by giving Life Steal AND Spell Vamp, while once again adding to your DPS and making those abilities just a bit more useful, and it's active can be helpful in putting out some extra damage. By now you should have sold your Doran's Shield to get money and/or make more room in your inventory. I get Trinity Force, it is an expensive item but everything it provides is very important to Poppy, and besides, there is no reason to let that Sheen sit around when you can build it into this wonderful monster. Last is Atma's Impaler, the Armor is always welcome, Crit. Chance never hurts but what i was after in this was the passive, with it's passive you should gain about 45 extra attack damage, not bad considering all the other bonuses you got with it.

EARLY GAME
With Doran's Shield you will be far from squishy, but you can't put out enough damage to really kill anything. You will want to stay back and feed off minions until. you get all 3 of your skills. After this you can put out a some damage. You will definitely want someone with you that can sponge up a lot of damage.

MID GAME
By now you should definitely have at least Sheen. This is when you really get to go around killing stuff. You don't NEED someone with you but it helps a lot. Devastating Blow can be used on minions for easier farming but only do this if there are no enemy champions in the vicinity. You are really good at taking down turrets so after it targets a minion get up in that turret's face.

LATE GAME
Now you will be a killing Machine. You can run just about anywhere you want. You are amazing 1v1 and can even take 2v1 in their favor, if you play smart (i'll cover that later). As long as the odds aren't stacked to far in their favor you can, at least, escape from anything. You should definitely have Wriggle's Lantern by the beginning of Late Game. Use the active on it to ward a major monster (i.e. Baron, Dragon, Lizard Elder) this way your team has vision of an important area on the map. This also allows you to see if said monster has spawned so you can go for that buff.

TIPS
*Paragon of Demacia can be used to line up Heroic Charge.
*Heroic Charge Can be used as a chase if needed.
*Diplomatic Immunity also cancels out Turret damage, this make you an amazing Turret Diver.
*Your innate ability makes you hard to kill as the lower your health is, the less damage you will take.
*Diplomatic Immunity can be used when running away to stay safe, put it on the furthest enemy within range then continue to run, afterwards you may even activate Paragon of Demacia to make it even smoother.

2v1 Strategy
You must be at least level 6 to pull this off as you need diplomatic immunity
If caught in a 2v1 decide who will deal more damage to you. Put Diplomatic Immunity on the OTHER champion. Kill the one without Diplomatic immunity then continue to the other one. (it's relatively simple.)
For example, you see Kog'maw and Pantheon coming towards you. Pantheon will typically deal more damage than Kog'maw. Put Diplomatic Immunity on Kog'maw (cancelling out Pantheon's attacks) Start attacking Pantheon, then when he is dead you can kill Kog'maw. This will make usually unfair ganks somewhat fair again.

I'll try to update this build with a little more later but this is it for now.