Fiora is pretty much like Yi and Udyr, get away with tons of movement speed, but with Fiora, you have need Catalyst the Attacker (ok bad wordplay there); you need a catalyst to get movement speed, you can't just do it whenever, that catalyst would be attacking with furor, your e, and perhaps phage 3 times, combined with ghost. Done right, by jumping around with your double q (to minions) and ulting when you're forced to, and blocking fatal blows with your w, getting hp with your passive, you can escape pretty easily with sufficient hp for baiting, and then turning back.

I don't like getting pots on Fiora because she's not mana-reliant and has passive for hp regen, but I see some that get flask or always 5 hp pots, which makes Culinary Expert good on her. You can always burst the enemy champ and get full stacks on your passive, taking minimum with your w, and using your second q to get out. Never get tiamat, go straight to hydra, the reason being, say you have little hp and you see a wave you can clear to get it back, if you splash without lifestealing, the wave's gone and you don't get much hp out of it, the only exception is when your behind and can only afford tiamat at level 6. Because your getting Youmuu's, you might as well get the gp avarice early.
I'm not sure whether you should get Frozen Mallet or Tri-Force, you have so much attack speed that Mallet gets wasted, but it's good for holding enemies together in your ult, I say, see how much sustain you need, because overall Tri-Force is better, it gives you crit for your IE and helps you escape with movement, you can proc sheen easily, and phage is really deadly for your movement speed combo. Youmuu is the best armor pen item for Fiora, because it's your only cdr item, gives crit and even more movement. Guardian Angel is the best defense item because even if they catch you, you have a second chance to jump away and escape.

The ability order is obvious, q before e because it has shorter cd, and more burst.

Just a standard ADC build

Get smite and ghost, and start with hunters 5 pots, getting razors (not wriggles), and then selling them later.