Hello,
This is a guide to a more realistic stage of Fiora. I know whoever is here has already seen the champion spotlight or had a couple of games versus "unskilled" opponents as an AD-Carry.
This is not the real case.. with the latest state of game full of tanky champs that also deal a significant amount of damage, Fiora is not really viable as a pure AD-Carry.

Note:

• The total health shown does not take into account a fully charged Warmogs and Masteries. Total health at lvl18: 4088
  
  
• The damage shown in champions stats above does not include bonus from Atma's Impaler (+72 attack damage)and bonus from Bloodthirster charged.
  Total build attack damage at level 18 is 407

Jungle:

Note: Jungling is possible without smite, but i am strongly against it. The reason you take smite as a jungler is to do it faster, keep up with other player's levels, secure kills on dragon/baron, possibility to steal enemy jungle buffs while they are at them etc.

Lane:

Note: You can use Ignite during the animation of Blade Waltz for more secure and burst damage.

If you decide to play Fiora as a Jungler i recommend:

9 x Greater Mark of Attack Speed
9 x Greater Seal of Armor
9 x Greater Glyph of Cooldown Reduction
3 x Greater Quintessence of Desolation

Short explanation:

• Greater Mark of Attack Speed works well with Vampiric Scepter
• Greater Seal of Armor for safe jungling and ganks versus AD champs
• Greater Glyph of Cooldown Reduction. Fiora's main heavy damage skill is her ulti. So this + 4% masteries = better chance to have it available when needed
• Greater Quintessence of Desolation AD champ with no brutalizer in build

If you decide to go Laning with Fiora i recommend:

9 x Greater Mark of Desolation
9 x Greater Seal of Armor
9 x Greater Glyph of Cooldown Reduction
3 x Greater Quintessence of Desolation

Masteries are rather obvious. I will explain a couple in more detail.

• 4 points at Sorcery : 4% + runes help have your Blade Waltz available faster.
  
  
• Demolitionist : I guarantee you there will be moments that you will be left alone with a turret. This works well with Burst of Speed
  
  
• NO points at critical strike damage/chance because your main concern is high attack damage and lifesteal due to high ratio on Blade Waltz
  
  
  
• Point at Veteran's Scars for happier jungling

In both Jungling and Laning cases the items remain the same. I will explain why.

1. Start with Vampiric Scepter. It will help you jungle easily and avoid spending gold on potions and works well with Fiora's passive ( Duelist ). In lane it will help you get some last hits on creeps without the pain of range champs harassment and most important of all: When you hit lvl 6 and there is a chance for a kill, you can hit your ulti even under enemy turret, get the kill and walk back to safety like a boss. If you havent used Lunge to get in position for the kill, you can also use it to retreat if there are enemy creeps behind you.
   
   
2. Next buy Boots and Long Sword. If you have enough gold finish Mercury's Treads and Wriggle's Lantern.
   Reasons:
   - Even if the enemy team is not packed with heavy CC you can't afford even the slightest disturbance at mid-late game right before you hit your ulti in a teamfight (and get Pentakill;) )
   - Those boots combined with lantern will give you enough Magic Resist, Armor, Attack Damage, Life Steal and bonus hits on creeps to be able to stay in lane for 3 weeks, or go disrupt enemy jungle or get Dragon if you have the chance to leave lane ( Yes, with these 2 items you can solo dragon with ease ) + free ward for dragon or bot lane.
   
   
3. Next comes:
   Black Cleaver : A lot of AD and the penetration effect that works well with Burst of Speed and Blade Waltz (since her ult applies on hit effects 5 times)
   Vampiric Scepter : Get this for more lifesteal and as a component for a Bloodthirster later in game. Do NOT make this a bloodthirster yet even if you have enough Gold. You will have a lot of damage, but you wont be alive to apply it....
   
   
4. Fun starts here:
   Build a Phage and if you have enough Gold rush it to Frozen Mallet. This is my favorite state of Fiora. This item give you the survivability you need + free Slow to Lunge and Burst of Speed their poor squishies trying to flee combat.
   
   
5. Finish your Bloodthirster. Now you are in condition to actually roam free and kill whatever you step onto.
   
   
6. Late game. This is the part where both teams are left with just the inhibitors. Go get yourself a Warmog's Armor and Atma's Impaler. Congratulations you are now indestructible and your damage is as good as French wine.

In short:

Mid-Game:

• Mercury's Treads
• Wriggle's Lantern
• Black Cleaver
• Vampiric Scepter

Late-Game:

• Mercury's Treads
• Black Cleaver
• Bloodthirster
• Frozen Mallet
• Warmog's Armor
• Atma's Impaler

Again in both Jungling and Laning

• Start with Riposte
  - Jungle: evade 1 attack + return some dmg back to monster + bonus Attack damage from its passive.
  IMPORTANT: when jungling watch the animation of the monster you are insterested to kill faster (Ancient golem, big wolf etc) and right before it hits you activate Riposte.
  Reason i am saying this: the evade+hit back effect lasts for 1.5 sec only, so you must take the hit in that duration. If you hit Riposte long before the monster attacks you, the effect will wear off and by the time the hit actually lands.
  
  - Lane: Bonus attack damage helps you start last hitting creeps easier. The active helps you annoy the hell out of your possible range AD opponent as when they ll get in position to harass you, you hit reposte and they harass themselves instead ;)
  
  
• Jungle: Next unlock your E ( Burst of Speed ). You will need it to jungle faster and regenerate some health faster in order to be ready to gank a lane any time required.
  At level 3 take Q ( Lunge). This is a must in order to gank. Come from the sides, Q to a creep, then again to the targeted champion hit Riposte and Burst of Speed at the same time and watch them flame on chat. When you come out to gank, they will either run (in which case burst of spee + Red buff wont let them go far) or they will turn to you and attack you ( where your Riposte will block the first melee attack and poke them back). Note: make sure the enemy creeps are already focused on your creeps when u go for gank and plan to hit Riposte at start, otherwise it will go wasted and parry on some creep.
  
  
• Laning: At level 2 take Lunge for easy harassment and possible kill. If you have a jungler in team, make sure to Lunge when he comes out at the same time and suprize your enemies with a well coordinated gank. At level 3 take Burst of Speed
  
  Skill priority:
  1. Max your E ( Burst of Speed ) first, as this is your main damage source. A Must for pushing - downing turrets - killing AD melee's that think they outdamage you and suddenly you pop Burst of Speed and *censored* them ;)
     
     
  2. Max your W ( Riposte ) 2nd for the nice attack damage boost it gives.
     
     
  3. Max your Q ( Lunge ) last as this is only useful as a gap closer.
     
  
  
  

You basically follow this patern in every teamfight as its the best way to get the most out of your champion:

1. Lunge into the fight targeting the tank first and then Lunge again to any of the rest with preference to the enemies that don't have flash or built-in fast escape mechanism.
   Explanation:
   - Target tank first because in teamfights the tank is usually in front of his team and easily reachable since it wants to initiate the fight. You are going to spoil that for him though;)
   - Second dash to an enemy that cant escape because you do NOT want to scare any AP/AD carrys away. You need them all in range for your ulti.
   
   
2. Hit Riposte as you want to avoid the first attack/on-hit effect attack that's headed to your face once u appear on their doorstep.
   
   
3. Blade Waltz on a squishy enemy without flash or high mobility.
   Reasons:
   - Your first target receives the first and the last hit from your ulti. Thats 2/5 guaranteed hits on a squishy enemy = may he rest in peace.
   - Your target must NOT have any flash or mobility skills because when your ulti ends you will land next to your initial target. That means if he flashes/moves away under a turret or too far from your team, you are basically dead or too low on health(after they beat the "poop" out of you) to get back in the fight and help your team.
   
   
4. Once Blade Waltz ends you must have regenerated a LOT of health due to your lifesteal's synergy with it. Now hit Burst of Speed and start chasing/killing leftovers from the Armageddon you previously unleashed upon them.

After the latest patch you can pretty much do anything you wish in jungle.
Aside that i advice the following:

1. Start with Wolves. You will clear them at ~1:55-2:00 depending if you used Riposte successfully or if a teammate helped you with some damage or pull(leash).
   Note: If you decide to go with a pull, make sure your teammate pulls them from the side the Blue Golem is, otherwise they will run to him fast towards the mid lane and you will lose time to walk to blue once you kill them.
   
   
2. Continue to Ancient Golem(Blue buff) again with Riposte focused on Golem's attacks and use smite when its down to ~445 health. Once its dead you have leveled. Unlock E ( Burst of Speed ) and hit it immediately to finish off the 2 small lizards and regain some health back.
   
   
3. Go and clear Wraths. Tip: Spam Riposte and Burst of Speed at the same time to have them both available faster. I often see some junglers waiting for each skill's effect to wear off before activating the next one, which is a waste of time IF your skills dont devour mana and render you useless.
   
   
4. Go to 2 Golems. Unlock Q ( Lunge ).
   Note: It would be easier for jungling if you level Burst of Speed again, and get Lunge at level 4, but this leaves you unable to go gank at level 3 in case an opportunity appears or if one of your teammates dies and leaves his enemy on low health.
   
   
5. Go to Elder Lizard(red buff). Clear and go gank any lane is available. Make sure your team doesn't overpush their lanes as you dont have any sort of stun/snare apart from the Red buff slow. If you dont see a chance for Gank, go kill Wraths and Wolves once more time and recall for items.
   At this point you can get the following:
   • Vampiric Scepter (already owned)
   • Boots
   • Cloth Armor
   
   
6. Once you build Wriggle's Lantern go place the ward at Dragon, kill it and keep an eye for any enemy champion that comes to check/kill so you can go and say hello ;)

Pros:

• You get to watch a fine butt throughout the whole match
• "Tons of Damage" with your Blade Waltz
• Easy and pleasant jungling
• 100% success on ganks after you hit level 6
• High lane sustain (up to 3 weeks)
• Very tanky at mid-late game
• Very dangerous to be left alone with an enemy turret
• Able to make enemies go "Hah i got you now!! ....wait.. why is my screen grey??"

Cons:

• Relatively expensive build if game doesn't go as "ok" as expected.
• No escape mechanism apart from Flash.
• No cool skins yet apart from Royal Guard.
  

- This is it for Fiora. I hope this helps out a few players out there that want to try this champion. Note that this is my first guide so excuse me if i made any mistakes and any help to improve my guide would be most appreciated. I also apologize for any grammar mistakes, English is not my main language.

- If you have tried this guide share your experiences in comments bellow.
- If you have anything to add/edit any feedback is more than welcome.
- Please vote.

Edit:
- Thanx LustxFinale for correction on masteries, i thought builder had the same restrictions as the actual game.