Although the item build i put up is generally what i go for, realize that you have to be able to adapt to any situation. If there is an opposing Karthus in the game, you want to get a banshee's veil ASAP. Your second Archangel staff can be replaced by a rylai's scepter if your health seems to be dropping to quickly, or maybe even another Hat or Abyssal scepter. It all just depends on what is going on in the current game. If you can find a way to fit in some Ability cooldown reduction, that would be awesome. Post your other ideas, i am very open to criticism, and this is my first build.

Generally you want to mid if you are going to play this build. I have done it several times and have found that it is my favorite way to carry. Begin by playing defensively and make your opponent think you are incompetent at your position as carry. (after all, she is the deceiver). Generally by lvl 3-4 you should have your first kill depending on who the opponent is. I always feel real good when i find out it is Ashe, but be cautious of Ryze. If you haven't gotten your first kill by then, that is fine, don't push for it. Let them come to you. Stay mid until you have at least gotten your soulstealer, then you can help ghank if need be, however if your team is also doing well, just continue to farm and harass your opponent. Don't worry about pushing mid until you are about lvl 10. Just try to help out your allies when you can.

I like to use Heal and Teleport, but Ghost and Ignite are also good choices