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I go with an Elixir of Fortitude and 4 Health Pots as the initial item. The elixir gives you damage and health, while the health pots allow you to lane longer. I usually get first blood and a gank in the first 5 minutes.
Then I go back and get Berserkers Greaves and a Zeal. After that I try and rush a damage item such as a Bloodthirster, even if I have to buy all the items seperatly (starting with B F Sword). Then another Zeal, an Infinity Edge (same as the BloodThirster, buying items seperatly if needed) and build the Zeals to Phantom Dancers.
Here is where you can stray.
If the team is heavy tanks sell the Greaves since Phantom Dancers give movement speed and get a Black Cleaver, Last Whisperer (a must against tanks), and/or a Madreds Bloodrazor.
If they have heavy magic team, grab a Banshees Veil (a must against ap teams) and either a BloodThirster or another Phantom Dancer ( 3 Phantom Dancers plus an Infinity Edge = 100% crit chance).
If people are getting away or you are getting targeted, grab a Frozen Mallet for slows and survivability and another Phantom Dancer.
I use 22/0/8 Masteries
Quintessences: Armor Pen (for tanks)
Marks: Armor Pen (for tanks)
Seals: Mana Regen per level (so mana is not an issue)
Glyphs: Magic Resist per level (So AP people don't roll over me every team fight)
I grab Ghost and Exhaust to catch up to people/flee/slow them for either a kill (if both are used its pretty much garenteed) or to run (again, with Ult + Tumble an exhausted enemy and Ghost make you pretty much a master juker)