Not Updated For Current Season
Masteries: I go with a standard 9-0-21 build, using the flash and ghost masteries.
Summoner spells: I use the standard Flash and Ghost, both to chase, to dodge spells, and to get out of ganks. i don't recommend getting Clarity because i usually don't have much of a mana problem.
Get Rod of Ages or Sorcerer boots first
Situation: It depends if you are fed or not.
get Zhonya Ring or Lichbane first
Situation: If they are concentrating you get Zhonya for unique active and if not then go for lichbane.
Pick the 6th item depending on the match
Situation: if everything is going alright and you just want to nuke them down.
Situation: if they are heavy tanks i recommend this item.
Situation: If their team have super MR then seriously get this.
Sorry if I didn't write that much but i'm up to suggestions and improvements. Please vote and comment.