Poppy is a melee dominator. She will end up doing very ridiculous amounts of damage with Devastating Blow, Your main goal is to defend/capture as many points as possible, you want to be an objective player. Use Ghost right off the bat to get that extra speed boost to capture windmill, but do not forget to pick up the speed buff on your way to windmill.

Early Game:
You are going to be one of the fastest heroes so you should always head to windmill first off. Once there begin by begging you capture on your side, a bit away from the jungle, remember the extra .5 sec it takes you to get there is the equal time it will take an enemy to get there, and if your team is on the ball, hopefully they can run interference for you. Don't be afraid to break away from the cap to help kill the enemies though, but do so wisely, wait until you can get the stun off. I often find myself stunning and running past the enemies towards their spawn point, they will drop you and you can reposition for another run. After you take the windmill assess the situation. Remember, they will probably come back to try and take that point again, so if you are near half life, stick around, you will have time to grab 2/3 health boosts near the windmill before they arrive again.

Mid Game:
You usually aren't strong enough to take on more than 1 hero at a time, but can harass moderately well. At this point I like to continually attempt to defend / take windmill, with a quick 'b' to help elsewhere on the map. Don't overextend or chase to far, and remember, even though the jungle is great for pinning enemies, its a bad place to fight. Don't be afraid to run, you can outrun most people, and should be able to gather a few health shrines to stay in business. Near the end of this phase you should have nearly all the speed you will get (I've never completed a Force of Nature), so you can be much more mobile, and a much larger threat.

You are dominating force, you should be able to solo most heroes, and taking on smart 1v2 and even 1v3 situations should be something you can do. But remember, your goal isn't to kill heroes, but to take and keep CP's. I tend to focus on a triangle of three, and only once they start huddling together too much will I spread out and take another one. With this strategy you should be able to have enough control of the map (especially with decent teammates) that you should hold the majority of CP's for probably about 70% of the time, which is enough, unless you are very far behind, to win most games. If this fails, differ to a team based strategy as outlined in Dominion Guide: Roles and Teamwork.

pretty straightforward 21/0/9 build. The only real thing to note is the point in Haste. This is incredibly useful. By mid-late game you should be able to traverse the entire map if you properly use the speed shrines, your W ability, and ghost.

Poppy is best suited to a sort of Hybrid role, someone to fill in as a Taker, a Capturer, or a Disrupter. As she gains momentum, she'll soon be able to fill any roll well. Be prepared to break away from a push with an ally or two to disrupt that lone capturer, you should be able to get there pretty quick, and if you have the jump (which you should) you will likely score a kill and recap as well. Peel away and ghost across the map to secure a CP and keep them guessing. If you are fluid, you will be most beneficial to your team.

Ghost-This is a must! While a good choice in Summoner's Rift, it is so critical for the role Poppy plays in Dominion. It helps to make her ever present, which helps your personal score, your K:D ratio, and your teams Victory

Ignite -
I like this a lot as it can help you harass a few enemy heroes as they are capturing (the one ignited can't begin capturing while on fire); scare off that low-health champ that is harassing you and preventing the otherwise easy capture; allow you to get a kill so you can focus on another enemy, and more!
Other Alternatives:

Garrison - This is good as it can help you kill a couple heroes next to their CP, however I have found it gives me a little bit of a false sense of security, a lot of people will counter it with a Garrison of their own, and defensively it doesn't help much (because with two enemies, your tower shouldn't be shooting at either one)

Flash - Not a bad choice, but I find with Paragon of Dementia, Ghost, and the Speed Shrines you don't really need the extra mobility. Then again, there are a few deaths that could have been saved by a good flash.

Cleanse - I like this one too, especially as people begin to work on teams a bit and get some more CC than what I am typically seeing now.

Exhaust - Another viable option.

With Poppy in team fights, your main goal is to be the tank role, so choose the strongest biggest annoyance of their team, and use Diplomatic Immunity to render him useless against you, decimate him/her! Then, try and hit those tackles against wall's as much as possible to stun them. W>E>Q>R