Fiora Assassin Mid is definitely an off-meta pick, but if you master it I can guarantee you that you can surprise many people. Most people don't know how to counter Fiora Mid because it is mostly not a great pick in ranked in their opinion (especially low-elo), but it has it's perks. My name is Mackindaw, but my Summoner Name is Vel0city. Add me if you would like to see how awesome Fiora mid is. I am a mid-lane main myself, so I hope you enjoy this guide and learn a lot :P

Pros

Lifesteal can save you in tough situations
You can win trades so easily
Great mobility
A lot of different escape techniques
Pretty much unstoppable in late game if you are pretty fed

Cons

Mostly squishy early game and mid game
Very hard to win in tough matchups
Can be easily shut down if you are camped

Flash is a no-brainer. You should always take flash to escape most ganks if you have Lunge on Cooldown.

Ignite is my preferred summoner spell in mid, but Barrier is neat if you are against poke champions or burst champions. Riposte is a great tool, so most of the time it takes over the role of Barrier.

Duelist's Dance is what we need to pay attention to the most. Whenever you have a passive vital up on the enemy, always look to go for it. Also, if you don't know yet, a little tip is if a vital pops up on the enemy that is behind them and/or you don't like the angle that vital is at, just walk away until you are out of range, then walk back to reset the passive. This is a great trick to use when you want to play passive or if you are against a hard matchup. This trick definitely defines a good Fiora player versus a bad one.

Lunge is a great tool to escape, but also an amazing way to deal crazy amounts of damage. If Duelist's Dance is up on the enemy, you should always look for a nice Lunge onto it for the awesome true damage it deals.

Riposte is a great tool to prevent any cc effect. Try to challenge yourself to only use Riposte effectively. Because blocking auto attacks is a great way to survive, but blocking cc is an even better way to survive.

Bladework is a key ability to Fiora's kit. With your crit damage runes, this ability will do tons of damage. Use this to execute the enemy as a killing blow.

Grand Challenge is a very useful team fighting ability. This ability can help you make outplays in tough trades. I would use this a lot, especially if some of your teammates are behind. The enormous amount of healing is what makes this ability unique, so use it wisely.

Fiora is definitely a great champion to play in ranked. I would recommend if you are just starting her to play a little bit of normal games top lane first. You have to know the basics in order to master this build. I will admit, this build is HARD to master in ranked. I remember just trying this build for fun in ranked, and I actually climbed up from Bronze 5 really fast with her. If you want to carry games in style, then Fiora mid is the way to go :P.