Like WyldeFyres mentioned, early on it is about using your Q to proc Vitals, so "poke" with your Q, parry CC/use E then auto to slow, crit, then by this time you could probably Q away, preferably onto an enemy minion to lower Q's cooldown ( you can switch the order in which you use W and E but always try to save W for CC if any). I always take ignite to get better kill potential early on, and it works so well with your ultimate, dat true dmg. I love going up against champions with CC since I feel it gives Fiora an advantage in a duel with them (W).
With her Ultimate: if I take flash I will most likely blow it on getting behind the enemy to proc that vital point, since it willll be the hardest one, usually. I prefer taking Ghost since it has a lower cooldown, and it helps so much in proccing those ultimate vital points :3 . So, with Fiora's ultimate, E (slow), and ghost, I can force a flash or outright kill the enemy, and that's not even mentioning ignite. If they are overextended I do not need to use ghost and they will still use flash if they want to try to live.
As for the build, like WyldeFyres said, Tiamat to Hydra or Black Cleaver. I really like building Fiora defensively after Hydra, preferably Spirit Visage or Frozen Heart. Hydra helps way more in lane, with the minions there to life steal off of, its damage, and how it makes farming way easier. I have tried Blade of the Ruined King, but in top lane armor is built against me, so I feel Black Cleaver is better for more damage. In short, Ravenous Hydra is great for Fiora, so you cannot go wrong with it as a first buy ( I have yet to try Titanic Hydra on her though, might help my defensive build some) . After Hydra/black Cleaver, usually just defense, but if I am fed I might get a Youmuu's Ghostblade. thats all I know, glhf!
