It's my first guide ever and it's about my favorite champion: Fiora.
Fiora relies pretty much exclusively on her auto attacks and her ultimate so she's very sensibile to crowd control.
I ask you forgiveness for my writing and my english

Duelist enhances your health regen as you deal damage to foes, this passive stacks up to 4 against champions.

Lunge allows you to dash twice to a foe dealing some damage, the second cast is free and it's this cast that starts the cooldown. Lunge applies hit effects like the Burst of Speed stacks and the stacks from The Black Cleaver.

Parry passively increse you AD by 15 at rank 1 and by 5 at the other ranks up to a total of 35. Parry blocks damage from the next auto attack of a champion, siege or super minion and big monsters. Parry blocks pretty much all the empowered auto attacks, like Siphoning Strike, but it doesn't block any eventual crowd control.

Bust of Speed increses you attack speed a lot for 3 seconds and each auto attack will gain you a stack of movement speed, based on rank of the skill, that stack up at 3. Kills refresh Burst of Speed cooldown and assists halves it.

Blade Waltz allows Fiora to dance through the battlefield while dealing physical damage to enemy champions in range. This ultimate is a powerful bust with a couple inconvenience,some of them you can use them and some you can't. Invisible champions will be hit if inside range but the first strike won't deal damage to them, this should be true also with champions inside bushes. At the end of the dance you'll be near the first target of the ultimate so be cautios because the enemy could get you in a thight spot, under tower, etc. Each strike of the ultimate applies on hit effects as life steal, Hydra passive and Black Cleaver' stacks.

If distant from your foe, open the assault with Lunge, Parry and Burst of Speed since both lunges count in your movement speed bonus and Parry helps blocking an auto attack.
It would be better use your ultimate as a finishing blow or to avoid a great income of damage since you're untargettable, plus it applies the stacks of The Black Cleaver to every enemy hit.

Pros: Cons:

Godlike mid to end game Kinda squishy
Shreds entire teams Must be very careful in teamfight
Very strong pusher Has a quite difficult early game against the aps
Life steal monster Mana hungry in the early game

Try to roam mid after the first tower if not earlier but if you're winning the lane you should not have any problems. After the first tower, if you're playing in the upper side of the map, you should go check the enemy's blue buff to balance your mp and cdr.
During teamfights try to flank the enemy team or to join a little later the others, by doing so you'll avoid most of the enemy crowd control. Always focus the squishyest of the targets so tha you can refesh burst of speed and keep your damage going.

Every champion is viable, it's just more or less difficult to get going