First things first, when in loading screen, try to pick the target you gonna use DI (diplomatic immunity) on. Most of the time, it will be the enemy tank who has no taunt or CC. (Dont pick rammus <.<) By doing so, we will know whom to DI, and whom to engage second and third.

At this phase you ll have enough time to consider your tactic. Lets say, enemy has 2 AD, 2 AP and 1 tank champions. (and lets say tank is not shen or rammus).

The main strategy for this build is, using DI on an enemy champ, then kill as many enemies as you can before DI wears off.

Second thing to know; getting the BLUE BUFF before team fights. This will maximise your damage output.

Item order is just as shown. Only thing you should decide is when to buy vampiric scepter. You can buy it whenever you think its best.

What do we want in early game:
we want to get as many creep kills as possible while taking least damage. Taking least damage is important because as poppy is so bad at creep kills, we want to stay in the lane as long as we can. Hug tower if necessary. Dont be a hero (yet!). Dont charge in unless its certain kill.

@ mid game;
In early 5 men tower pushes, your goal is to kill at least 1 enemy, and then if lucky get out. Imo its ok if you kill and die. At this stage, its almost impossible to get double kills, wihtout ally help.

@ end game;
This is where we shine. The longer the game, the chances of you winning rises. This is because,
a) when you finish your equipment build, not even tanks can handle your damage output.
b) 8 seconds of DI, will be more then enough to get you a double kill without ally assists.

In end-game team fights (including tower dives if there are any), what we do is, basically, remember which hero we picked on the loading screen. We get close to the enemy group, then use DI on the hero that has least burst damage or tank.

After using DI, the clock starts, we have 8 seconds. use "W" to get max buffs, and "E" to any carry you like, preferable, the most fed or highest burst damage mage.
Charge him, then spam Q and basic attacks till he is dead. which should be in 2 or 3 seconds.
Most of the time, he will be dead, before he know it.

now we have around 4 or 5 more seconds of immunity. charge to the next closest carry/mage, repeat the treatment.

At this point you can;
a) keep fighting, and assist your team on the rest of the fight,
b) run away.

either way, its a fast 8 sec run, up close and personal.

Pros:

Excellent tower dives
Excellent combat initiater
Amazing at end-game

Cons:

Terrible at creep kills

1) Study your enemy at the loading screen.

2) Try to stick to the plan. DI the tank, kill the carries/mages.

3) Be patient on creep kills.

4) It is ok if you die 10 times before 30 mins. Keep farming, keep getting exp. You know you ll rule the end-game.

NOTICE: people will try to run away when you DI, so try to chase the enemies that dont have an escape method. So best method sometimes can be, joining the fight behind enemy lines (evil ?!)

Hope you enjoy this build
GL & HF