DO NOT push your lane. Passively farm to gain distance from their tower therefore giving you more chasing capabilities. This is good for fiora as her dash gives her 2 stacks on her E if activated enabling her to have extra movement speed and attack speed for chasing.

Rome around from top and mid or bot and mid for early burst ganks , Fiora's E , Q , Q , R gives her a nice nuke for an AD melee enabling the other AP carry mid enough nuke to gain a quick kill. Aim for squishy targets in fights such as AD carries or AP carries as they are easy to kill and output the most damage , This isnt a hard task for fiora as she is a sustained fighter and has a nice gap closer.

Now you are a tanky beast you deal damage and have sufficient HP to fight all carries who challene you. In a team fight you should enter late. Although you are tanky the CC will kill you and the AOE damage should shred you as your armor and MR should be low and your high HP is just for scaring people. When dueling someone do not use your ult unless you are chasing someone who is quicker than you or you are losing and you need some sick life steal.

I recommend taking Flat AD marks and quints as early game you can be un fightable and be tanky by taking flat Armor and MR per level.

Boots + 3 pots.
Wriggles lantern.
Phage.
Beserkers Grieves.
Frozen mallet.
Wits end.
Warmogs.
Atmas impaler.