This is my first MobaFire guide. I decided to create one for Fiora right now because I am currently maining her for Top and Mid lane. I have also come up with a build which I deem very effective for her so... This happened.
Anyway.
I hope this guide will be helpful and effective! If you have any suggestions, don't hesitate to leave some in the comments!
Let's go!

Hi, I'm LTG.Mega! I main Assassin/Mage/AP Carries and I live in the Mid Lane.
I discovered a while back that Fiora mid works, and with some calculations, I thought that she was great for mid lane! Especially after her rework. :3
Although I did think she could be used in mid lane, I never thought of trying her until I got rekt by an enemy Fiora who went up against me.
And so, I tried her...
AND HOLY POROS SHE'S AMAZING IN MIDLANE HOLY SHEET
Overall,
Fiora has great poking abilities that come with ensured safety thanks to the Vital proc.
Additionally, she is equipped with a great, freelance Lunge that is now able to give you more opportunities and choices thanks to it being more skillshot-like. Yes she can escape now!
Her parry is crazy though. It's powerful, but it can be contained. What do I mean?
WELL
Although her Riposte can parry 90% of the possible damage Fiora can take, it has it's weaknesses.

1.)You'll need very precise timing and prediction
2.)Enemies can force you to use it
3.)It has a limited range. Champions with skillshots that have massive range won't get the stun or damage.
4.) It will block all non-turret damage affecting her during the 0.75 duration, but will only stun the first hard CC caster within range if there is any. Additionally, when she stabs, the movement speed and attack speed debuff will only affect first champ hit.

So there. Sure, it's OP at times, but it's manageable.
Moving on...
Her third skill is pretty awesome! Because basically, it's two things:
-The first boop on the head is a slow that will never EVER crit.
-However the second one WILL crit and deal some bonus damage.
Plus attack speed buff!
Both head bops apply on-hit effects.
AND, it resets her attack timer. :3
And the Grand Challenge
Yes, she sees all your Vitals!
It also passively increases movement speed you get from Duelist's Dance upon hitting them regardless whether the opponent is challenged or not.

So there you have it! A plain look at Fiora's kit and advantages and stuff.

Now, Fiora is meant to be a duelist. That means, she exceptionally excels at 1v1s, and single targets. With that being said, she also needs to wield some handy sustain, as well as to have quick reflexes and to be fast on her feet.
So, she was blessed with small bursts of health and movement, a small but ample amount of mobility range to stay out of danger, and quick fighting tools to get ahead of her opponent.
Unfortunately, she does not perform well under multiple hostile pressure, like ganks, 1v5s, and most probably opponents greater than 1.
And that's because Lunge, and Grand Challenge are designed for single targets. And like, those deal the greatest damage (aside from her basic attacks) so those are her key abilities. Riposte does have a chance of keeping her alive, but she'll be in the same place for 0.75 seconds, and that's like, enough time to formulate a dead end for her. The Vitals are just extra things that make attacks stronger. Yeah they mark all opponents in sight, but eitherway you can only hit one.

~~~AND THAT'S WHY~~~

She's great for Top and Mid because she only fights one opponent for a significant duration in the game which is the Early Game.

Now that we know her traits, let's check out what we should build on her!

Due to her characteristic of thriving in battle, we need to equip her with:
Enough damage to fight back.
On-hit sustain
Something to keep that sustain happening
And most especially presence of damage output

Did you grab a hint?

That's:
Physical Burst Damage
Lifesteal
Attack Speed
Cooldown Reduction

Why?

Okay let's talk about the burst

Explicitly, it speaks for itself! Tons of damage.
Fiora is going to rely on her damage output to be able to take out her opponent ASAP. That's why she'll be needing it. Her greater damage dealers also rely mostly on her bonus AD so pretty much, you are gonna need to build lots of it to maximize the utility.

Next up is the lifesteal

Lifesteal relies on the amount of damage you do. Which is also why you really need that burst.

dat burst

How does it work? Well, say for example you have 20% Lifesteal. If your basic attacks deal 300 physical damage, you heal for 20% of that.
Basically 20% of 300.
So there. You'll need it to be able to stay alive while fighting Worthy Opponents

And then the attack speed

Well of course, you're going to want to keep that health coming right? Best way is through rapid head bopping.
Especially since you want to go around your opponent hunting for Vitals, might as well hit them with every click you make, right?

Strike quickly. Strike deftly.

Finally, the cooldown reduction

Overall, her abilities would take this long before you cast again (with 40% CDR)
Lunge - 4.8 seconds
Riposte - 9 seconds
Bladework - 4.2 seconds
Grand Challenge - 42 seconds

Fiora's Lunge has its cooldown reduced by 60% when you hit any enemy.
The way I see it, if you had 40% CDR and you hit an enemy with Lunge, it would be as if you had 100% CDR.
From computation,
At max level its cooldown is 8 seconds. With 40%CDR, it becomes 4.8 seconds.
Once you hit an enemy, its cooldown is reduced by 60%

Giving you a potential 1.92 seconds before you can cast it again!

8 ---> 1.92

AMAAAAZING

bonus AD thus adding numbers to your AD scaling abilities already, and will give you AP which is essential for your Riposte.
The Oppression is great because it synergizes with your already existing crowd control from Riposte and Bladework making you deal more damage.
Battering Blows basically gives you that much needed early game penetration.
And finally, Fervor of Battle will enhance your attacks the longer you stay in battle. Especially when you're farming and your opponent decides to poke you, you'll make sure to punish them for disturbing your peaceful cs-ing. That's because you gain stacks of Fervor for hitting any unit.
Recovery Tough Skin Veteran's Scars and Perseverance are going to be your best friends when it comes to sustain because of the damage block, bonus health, and super useful health regen.