I bought Fiora when she came out and by far is my favorite AD Carry champion. She has amazing burst and has a fantastic skill set which makes her very deadly. Especially with her ultimate together with lots of tiamats. Here is some very basic information about Fiora:

Melee, Carry

Health: Average
Attack: Strong
Spells: Weak
Difficulty: Medium

Your role as a tiamat Fiora is important to learn. A tiamat Fiora's role is to kill everyone as fast as possible in a teamfight. You have to time it perfectly when the enemies are closest to eachothers. Then you rush in and deals tons of damage with your high attack speed. When u hit low on hp, u just use your Blade Waltz and kill everyone almost instantly if they are close to eachother.

After you are done with your build. One thing you have to remember. Sell your Wriggle's Lantern and buy a weapon of choice. I like to buy Bloodthirster or Infinity edge. Another item which is really good with Fiora is the Black Cleaver.

Stay in lane and farm for your Wriggle's Lantern. Get as many cs as possible to be strong mid/late game. Try to harrass and get some early kills if possible. After getting som more items (maby 1 or 2 tiamats), you can start getting high killstreaks if you attack two or more at a time because of the Tiamat passive. When you have got the whole build you can almost just go alone against all 5 enemies and ulti and you will kill all the squishy champs, maby also some stronger.

Good luck ( but I dont think you need luck to win. )