Gliphs and Seals are the normally defense runes for and ad carry and Marks with Quints for armor penetration will make your early game easy.

The masteries, I say, are the normally masteries for ad carry but the most important is to get FRENZY in those masteries for MEGA ATTACKSPEED!

The items are more for pusher but it will help you at backdoor or some ***** like that :D but anyway the Doran's Blade can be replace with boots and some health pots. Then The Attackspeed starts with Berserkers Greaves then Statikk Shiv and Runaan's Hurricane. So after the attackspeed is secured we start with damage and lifesteal with The Bloodthirster, Infinity Edge and another Bloodthirster. Statikk Shiv and Infinity Edge was a good choice because I use Frenzy in masteries.

The skill sequence is simple :

STUPID MEGA ATTACKSPEED, SLOW, ESCAPE MODE AND BONUS INGITE

FLASH is good for escape ( with Rocket Jump, Buster Shot and Flash it will be a HUGE DISTANCE between you and your chaser ), but it will help you in chasing too if your enemy is too fast.
IGNITE is a good spell to make your first blood more easy to get and your early game will be easier.

Tristana can be an ap carry too but I like much more the ad carry version. She can be like jump, hit, kill and jump again. She's almost like "right-click to win" so it's easy to play as her.

Pros
-Fast killer
-An excellent farmer
-Bunny Hopper through the map

Cons
-Squishy
-First target in a team fight
-Vulnerable at CC