I use this build for personal reference, feel free to use it.
I really enjoy playing with her but at the moment you will find that Fiora will get banned alot in Normal or Ranked Draft games. it is a shame.

Of course she is a strong character and almost unbeatable 1v1. But you need to know what you are doing and don't lose yourself in the chaos of LoL that can occur on the battlefield.

This guide will focus on a build that I find myself using in the Jungle alot. And it works for me. If we win or lose the battle, I am usually still in the positive numbers.

Fiora is a really good ganker. Not because of her CC, because she has none, but because of her attack speed and surprising survivability. She can come back from extremely low health to making double kills.

You will notice that most enemies will try to kill you because of your low Healthpool. And yes, you will die quite fast. But what they forget is your passive health regen that stacks 4 times when hitting a champion. You can even turret dive champions as long as you can attack with Burst of Speed and have at least a Scepter of Life. Just remember that the % scales off your damage output ;)

I realize that this is not a build that anyone would take. All I see nowadays are full tree builds. Like 21/8/1 or whatever. I don't see the benefit of going that deep into a mastery if you lose so much utility by doing so.

The runes are also explained a bit more further down. Just a little bit. I don't want to type to much ;)

Anyway, enjoy this little guide/playstyle explanation and ask any questions you might have in the comments. Any suggestions are always welcome.

Pros:
- Great damage output
- Underestimated
- Passive heal

Cons:
- Squishy
- Prone to CC's
- Ulti needs your brain to function

10/11/9
Why do I use this Mastery Build?
Well actually I only use it for the following skills.

Alacrity
Attack speed is always nice. And when it leads to Weapon Expertise , it is worth that extra point.

Bladed Armor
Always handy when Jungling.

Swiftness
Gives you the edge in early game ganks together with your early boots of speed and with 1 more point you get your Runic Affinity . I often find myself living on Red and Blue buffs so it never hurts to make them last longer.

Greater Mark of Desolation
For Armor penetration. Speaks for itself.

Greater Seal of Armor
Extra Armor never hurts, especially when you are squishy.

Greater Glyph of Magic Resist
Same goes for Magic Resist.

Greater Quintessence of Attack Speed
No need to put too much into attack speed runes. 3 Quints will do the trick for a stable 10% @ start.

Of course there are more options in runes and you are welcome to suggest or just use them.

I don't know how this copy paste skill thing works, but it is quite obvious that Riposte is great to jungle with. Or at least, at the start. The cooldown is nice and short and the big monsters are pretty much slapping themselves to death.
Besides that your overal damage increases due to the passive AD increase of this skill.

You can solo Blue at lvl 1 with 1 potion and smite using Riposte.

After that it is up to you really.
I prefer to take 1 point in Burst of Speed after that and then one more Riposte before going to Lunge and the rest.

After my first Lunge I will focus on upping my Burst of Speed first.
Of course you take your ulti as soon as it is available.

Talking about your Ulti:
Blade Waltz is an extremely powerful skill!
It says that you are untargettable but do not forget, you are NOT immune to damage.
Example: Fiddlesticks casts his Bountiful Harvest on you 0,5 sec before you pop your ulti. He will simply keep draining you.
The same goes for Ignite and all other Damage over time effects.
Oh and don't forget Area of Effect spells like that big thing from Nunu & Willump

Besides that it is just more powerful if you use it on 1 or 2 champions than when you use it on 5.

I hear you think.

"Why don't you go for Wriggle's Lantern?"

To be honest, it was an accident. But I think this just works better.

I start off with Cloth Armor and 3 Potions. I run in the Jungle and do my thing till I finish all my potions. Then I go back for Boots and 2 more pots. Kill Red buff and start to gank at lvl 3.

Now you have 2 options. Go for Madred's Razors or for Ninja Tabi. (or Mercury's Treads if you are up against an AP heavy team)
Whatever your choice is. The other item of the 2 is up next. You should have 1 or 2 ganks already and you can buy your Scepter of Life around this time.
And then you can start having some fun.

Build what you like. But I don't build Wriggle's Lantern for one simple reason:
Fiora applies On Hit effects incredibly fast. Once you have Madred's Bloodrazor it is pretty much gg for anyone that you encounter 1v1. That is also why I build Black Cleaver Quite early and before Bloodthirster.

Anyway, you will find your own roll with the items you prefer.
If you find your Red buff getting stolen a lot or if you cannot have it for whatever reason, it might be a good idea to go for Frozen Mallet sooner.