A Fiora played on-hit needs rely's on her ult for killing people and is a very strong farmer with attack speed and Tiamat. Her ult applies on-hit effects, like lifesteal and Black Cleaver's armor shred. Items like Tiamat and Wit's End are very effective on her, while Madered's damage also applies on her ult. Tiamat makes her ult splash, making it destructive in small skurmishes. Stacking Tiamats can also be effective on her.

Attack Speed Marks help her in early fights, Armor Seals are very helpful in early game, due to the bonus durability, while MR per level Glyphs can help her late game. AD Quints also give her a lot of early game damage, combined with Riposte.

21-9-0 help her in late and early game, with extra damage and durability.

Starting with Boots of Speed, you can easily chase enemies or escape gangs. Rushing Berserker's Greaves and Wriggle's Lantern give her a lot extra early game damage.

My 2 core items are Tiamat and Wit's End, giving me a lot of damage, surability and farming potential.

My 2 final items are Madred's Bloodrazor and Black Cleaver, increasing my damage to any target, while also giving a lot of damage to my ult.

I max Burst of Speed, giving me a lot of damage in small skurmishes. Riposte is next, as it gives me a lot of damage due to it's passive increase, and a little bit of survivability, as it blocks a basic attack and parries. I max Lunge last, as it is primarly a gap closer.