If used properly Fiora is a very strong melee carry able to go all the way down to basically no health and come right back up to full health again to destroy the enemy team.

The key to this is lifesteal and continuous fast attacking with careful use of her ultimate.

People will attack you, and in teamfights they will lower your health thinking they are going to kill you, even chase you as they have full health and you have 10% hp, only to find that you come right back and destroy them because they don't realize that they can't take your health down faster than it goes up. That's Fiora basically.

Pros:

Amazing in lower ELO
Hard carry
Massive attack speed and damage
Her lifesteal is like a juke basically
Excellent at 1v1 against most champs
Can turn the tide of teamfights
Great at sustainable jungling and counterjungle

Cons:

Not as effective in high ELO
Susceptible to CC - be cautious
Doesn't have CC herself - get red buff

Duelist - Fiora's passive allows her to get some decent regeneration on top of her lifesteal. This is key in her ability to jungle sustainably and helps her in fights. Attack speed complements this (given by items and Burst of Speed).

Lunge - The main use of this really is as a gap closer. It doesn't do more damage compared to your auto-attacks so don't just spam it while autoattacking, only use it to close gaps or to escape if you can dash towards an enemy unit while running away. Currently if you click it twice during the first lunge, it will use up both lunge charges so be careful.

Riposte - The passive on this is excellent, which is why we level this ability second. The active will block an enemy autoattack. Simple enough. For the most part just use this ability as you're getting hit, but if you can try to save it if you can for special autoattacks (like Nasus' Q). While blocking those special attacks is pretty $$, currently this doesn't seem to block things like Garen's Q or Xin Zhao's knockup :(. We put 1 in this to start off the jungle for the purposes of increasing our AD right off the bat and being able to riposte blue golem.

Burst of Speed - We max this out first due to the massive attack speed bonus and movement speed utility. Click it just after your first autoattack in melee range for the fullest effect. Do not click it out of melee range as it will not speed your movement speed up unless you attack. Also great to use just after lunging so that you can maintain movement speed when chasing the enemy. The cooldown refresher on kill (1/2 on assist) means that if you're on a roll you can keep this up constantly in teamfights.

Blade Waltz - Fiora's ultimate is a very tricky ability that you must use wisely. Of note is that it will *apply on hit effects* with each attack. This ability is key in Fiora's coming back from near death to destroy the enemy team.
*Do not initiate with this ability as it is a waste of its utility* Instead if you are getting focused or low on health, pop it and watch your health lifesteal back up while you deal tons of damage to the enemy team.
In teamfights: Also be careful who you target as you will finally land on whoever you target. You'll want to balance out who you target based on a few factors: escape, surprise, and chase. Your ultimate can help you escape from the radar in teamfights as people become confused as to where you went / where you'll end up, try and target someone who is in a position of tactical advantage (either in your team's vicinity or on the outer edge of combat), and try to surprise the team on your re-appearance. The key here is to confuse the enemy team and drop off the focus of attack & CC.
1v1 / Ganking: This ability doesn't have much range so be careful of that, but it can also be used as a gap closer in 1v1 *only as a last resort*. Also if you're tower diving wait till you get low health and pop this ability to let your health lifesteal/regen back under the tower and pick up the kill. The tower will lose focus of you when the ultimate begins. Don't initiate with this on a towerdive as it is a total waste of the utility.

When NOT to use Blade Waltz:

Don't use when initiating
Don't use when beginning a tower dive (use as your health gets low when towerdiving)
Don't use on a champ that can stealth (they will stealth and stop your ult)
Don't use on LeBlanc when her passive is still up (it will stop your ult)
Don't use on Shaco when he has his ultimate up (it will stop your ult)
Don't use on Vladimir or Fizz when they can pool or playful/trickster out of it.
Don't use on Jax when he can Dodge it.
Don't use on someone who will just activate Zhonya's Hourglass to be invulnerable to it.

Ghost - This is very likely the best choice on Fiora for a number of reasons:

To chase.
To counterjungle and escape sticky situations.
To solo push lanes and destroy towers with your Burst of Speed and get the hell out of there quickly.
To get into teamfights and ganks from the jungle quickly when you need to.
To keep in constant melee range during fights.

Smite - We're jungling, obvi >_<

Other Summoner Abilities

Flash - This can be helpful to get in range to Lunge quickly when ganking, but overall I prefer Ghost over this. If you're really having trouble surprising the enemy and getting in range when ganking try Flash.

Exhaust - If you find yourself really having trouble with the fact that Fiora has no innate CC you can try this, but I prefer to leave this sort of thing to other teammates.

Ignite - The use of this is for when you are lvl 6 and considering towerdiving. Fiora can towerdive effectively once she has her ultimate, so Ignite can help deal damage and pick up the kill when doing so.

Cleanse - If you're super worried about CC (which you should be) consider using cleanse. I don't find it to be that much of a help except for certain enemy teamcomps that involve a champ that has one super stun.

Vampiric Scepter - Start out your jungle with this item. This item alone will give you enough lifesteal to sustain yourself in the jungle and be able to gank. Cloth Armor and Pots is just a waste of gold on potions here.

Wriggle's Lantern - Obvious choice for most junglers including Fiora. She needs the lifesteal, and the additional armor and attack damage are very nice for a quickly built first item. Also the on hit effect will trigger a lot on minions due to her high attack speed.

Mercury's Treads - Fiora is very susceptible to CC, this item is helpful to prevent CC from shutting you down. If the enemy team has very little CC consider replacing this with Berserker's Greaves for the attack speed.

Vampiric Scepter - Yes, pick up another Vampiric Scepter right away. It's cheap and the additional lifesteal makes a huge difference in Fiora's survival in fights. Basically you want your health to be going up and the enemy's health to be going down whenever you're in melee range of someone.

Wit's End - Why Wits End? We pick up this item for a few reasons that are extremely helpful specifically to Fiora. First off its a very cheap item to build so you can build it quickly. Secondly the additional attack speed will increase your damage output and more quickly build your stacks of Duelist. Thirdly the additional magic damage on attack is very good on Fiora not just for her melee combat, but also because her ultimate *applies on-hit effects*. This damage will NOT be reduced on subsequent attacks of your ultimate on the same target. Fourth is that you will easily build magic resist stacks which will help your survival against things that Fiora is most afraid of: heavy burst magic damage, and Thornmail.

Bloodthirster - Additional damage (stackable) and lifesteal, built from the Vampiric Scepter you already picked up. We build this because lifesteal on Fiora is imperative. Getting stacks is pretty easy and effective at this point as well.

Black Cleaver - Attack Damage, Attack Speed, and Armor Penetration. Overall an excellent item that isn't as expensive to build as other options. Fiora absolutely needs all three of these attributes: AD is obvious, Attack Speed to increase her damage output as well as how quick she can lifesteal & regenerate, and some ArPen to counter armor that will prevent you from putting out enough damage to lifesteal your health back.

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Sixth Item (before swapping Wriggles for Bloodthirster)

The sixth item really is more situational than anything. I choose Guardian Angel because you might find yourself being focused and need that additional survivability. There are many options however.

Basic Choice: Guardian Angel - If you are just getting focused like crazy and can't get people off you, GA helps with that .. sometimes people won't even want to attack you when they see the halo because they know you'll just revive. Also since Fiora can come back from low health pretty decently this can cause the enemy team to lose focus of you long enough for you to revive and start to wreck again. This also gives you some additional armor that we lose when we finally sell our Wriggle's for another Bloodthirster.

Last Whisper - At this point in the game people may be building tons of armor which can be a real bummer to both your damage output and your lifesteal, and quite frankly start to counter you. This item fixes that very nicely.

Quicksilver Sash - If there is one superannoying CC ability that is always getting you in trouble, just get a QSS and counter it.

Bloodthirster - MORE LIFESTEAL!! .. Also a possible counter to Thornmail if that is giving you trouble.

Infinity Edge - If the enemy team isn't really building armor and you're just wiping the floor with everyone consider this item.

Frozen Mallet - If you can't deal with Fiora having no CC on her own, pick this up. I find the movement speed on Burst of Speed to be enough to not need this, but if you're more comfortable with having slow CC all the time as opposed to only when you have Red Buff then try a mallet.

Tiamat - It was suggested to use Tiamat due to its interaction with Fiora's ultimate. While you can certainly try this out, I don't find it to be worth it as it only works when targets are right next to each other, which is a rare occurance in the first place and is easily prevented by targets moving away from each other.

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After the Sixth Item, consider swapping Wriggle's Lantern for another Bloodthirster as a final step before you become an elixir-addict.

I won't say much on runes here. They are designed to give you a very fast jungle. I picked up this rune combination and use it for for jungling most of my jungle champs from someone who claims to have worked out the math for the most effective jungle. It seems to work quite well for jungling quickly and sustainably, so that's why I use it.

As for masteries, these are designed to give you lots of attack power (the offensive tree) while giving you the fastest and most survivable jungle. We make sure to put points into masteries that will help in jungling, like additional attack damage to minions, additional armor, damage shield, and lifesteal. Maxing out the offensive tree also gives us additional damage. We also put 4 points into cooldown reduction in the offensive tree because Fiora has some pretty long cooldowns at lower levels.

Pick up a Vampiric Scepter, and start at Blue Golem. We start with Riposte for the additional damage and protection in our first fight to make it go quicker and make us lose very little health. After Blue Golem pick up Burst of Speed for the additional damage in the jungle.

Next progress to wolves, wraiths, and Red Golem. After Red Golem pick up Lunge.

At this point you will be level 3. Lunge will let you begin to gank. You can either continue to small golems, or gank. Check the lanes and look for opportunity to gank, or continue to jungle.

Fiora is very sustainable in the jungle with just her Vampiric Scepter, so stay in the jungle until you feel you have enough gold that its worth going back to pick up some items (keep in mind that boots are especially helpful when ganking).

Keep in mind that it is always best to have Red Buff when ganking as Fiora has no innate CC. While Lunge and Burst of Speed are excellent at closing gaps and chasing, Red Buff really helps her pick up the kill. If the lanes you are ganking can help you out with CC you don't need Red Buff as much, but if they can't then it is very helpful.

While you have Ghost up, consider counter-jungling. Take out the big jungle mobs (big wolf, big wraith, big golem, red/blue) and leave the little ones. This will severely annoy the enemy jungler and prevent them from jungling effectively. Because you're Fiora you may very well be more powerful than the enemy jungler and able to catch him by surprise and kill him, but be careful of teammates leaving their lanes to help. Use Ghost to escape sticky situations in the enemy jungle.

Ganking

When ganking you'll want to make sure you can quickly get in range to Lunge at the target. Surprise them from behind if you can. Try to focus lanes that have CC for you so that you can just let the lane CC the enemy while you jump on and destroy them. After Lunging use Burst of Speed to increase your attack speed and movement speed for chasing. Pop Ghost only if you have to to pick up a kill or get in range quick enough.

At level 6 you can potentially begin towerdiving when ganking (when Blade Waltz is up). Keep in mind when towerdiving you don't want to initiate the towerdive with Blade Waltz, you always want to take turret aggro first and use your ultimate for survival: to get the tower off of you and regain some health while picking up the kill. Be careful as the tower will likely re-focus you after your ultimate completes unless it has switched to a teammate.

I'd like this to be an evolving guide. Please feel free to make comments on what you find effective and when, what you find ineffective and when, and what can be improved, as well as special situations that are not accounted for in this guide.

Thank you, and enjoy Fiora!