This is my way to playing Miss Fortune! It's based on auto attacks that crit ALOT and crit HARD!
It also uses the Impure Shots passive right from level 1 to harrass them right from the get go!
I hope everyone gives this build a go and has great success with it, because i know that whenever i play her this is how i do it and it always serves me well!

Pro
-Good Farmer (Make It Rain and Impure Shots passive)
-Deceptively Strong (Impure Shots)
-Runs like a BAOSS (good for chasing and GTFO'ing)
-Good harrassment!

Cons
-Rather squishey!
-Her speed can get reduced instantly with one hit
-She will be focused down in a fight
-Prone to ganking due to only a 1 sec slow and Strut disappearing in one hit

Runes, errr i'm not all that good with the whole rune thing if i'm honest so i just went for a typical AD carry build!
So i went for-
Greater Mark of Desolation - Armor pen is very nice with this build simply for the Attack Damage you'll be doing!

Greater Seal of Attack Speed - Attack Speed for this build is delicious, Impure Shots is going to benefit from these so much!

Greater Glyph of Cooldown Reduction - I prefer the flat cool down simply because you notice it earlier, plus it is nice early game for the Impure Shots active.

Greater Quintessence of Desolation - More armor pen!

Quite simple really, just attack speed, CDR, ARM PEN and extra DMG!

Teleport CDR is nice for ganks when your team wards their lanes etc. The extra XP is nice for MF because if you take Impure shots first like i allways do you can really hurt your enemies at level 1 causing them to miss out on early XP letting you outlevel them very nicely to get some mid game ganks.

The Good Hands is allways useful just incase you do die, especially at late game if you're in a losing situation you can get back out asap and push them back... hopefully. :D

Alot of people think that Teleport is a wasted spell but i completely disagree, if you have a team such as my usual team that uses wards then you can get som really nice ganks, especially as MF seeing as she is fast right at the begining of the game.

Flash is just usefull all the time, especially if you can force a losing fight into the jungle, MF with flash can get away from almsot anything, because when you flash away Strut starts to kick in and gives you the speed you need to GTFO!

Other Good Spells
Ignite can be nice for finishing off people early game for the extra gold for items to rape *****es quicker.

Exhaust, Enemy trying to escape? Not anymore they're not! Enemy hitting you hard in a fight? Not anymore they're not!

Ghost, Enemy chasing you down? NOT ANYMORE THEY'RE NOT!

Cleanse, This spell is awesome do not forget that!

Spells to NOT take! =]
Rally - THIS SPELL IS SO ****ING GOOD OMFG LOLOLOL! But seriously do not touch this spell ever...
Smite
Revive
Fortify
Heal
Clarity
Clairvoyance

These items just work for MF, the attack speed along with the Infinity Edge is enough, but when you do get that Black Cleaver you can really see your DMG jump up a notch, because with impure shots you hit harder each time and then the Black Cleaver helps your normal attacks hurt more anyway, so it's a win win. Plus with this build you'll be critting like a BAOSS too :D.

I have to say though there are times when i might get a malady JUST for that AP on impure shots... however i wuld rather use the build i have shown here!

Infinity Edge - Crit ftw, Damage ftw Crit Damage increase ftw! This item is awesome for her especially once she has the full build. i prioritise this as a first damage item over life steal due to tha fact of simply having more damge on MF is far superior (tried and tested).

Phantom Dancers - Crit chance ftw, Movement and Attack Speed ftw! The crit chance on these works in synergy with the Infinity Edge! The movement works nicely with strut and can stop her from being so prone to ganks.

Black Cleaver - This works very nicely with Impure Shots because it make her auto attacks hit harder whilst her Impure Shots increasingly hit harder, plus it passively gives extra damage and attack speed!

Vampiric Scepter - I get this item end game just for pure survivability, because you're going to be about to heal yourself right up with it.

Bloodthirster - Turn your Scepter into this if you have enough time jsut to help end the game with even more Damage out put!

The Reason i don't get a Frozen Mallet in this build is because i constantly get Blessing of the Eldar Lizzard (Red Buff). ALSO, with the FULL build you're going to be hitting so hard they generally don't get a chance to run away xD.

I go for Impure Shots first simply because you hit hard from the begining of the match! Also i goes very nicely with Attack Speed which is why you get the Beserkers Greaves first!

Double Up is good to focus aswell because of the pure damage output in one hit, plus in a team fight it's going to hit two players really hard, also when chasing down an enemy it is a great last hit tool!
PRO TIP! - Hit a minion which is in front of an enemy, because it will bounce to the enemy player and hit them for more damage!

Make it Rain is awesome for clearing creeps, slowing a creep wave, slowing an incoming enemy for an easy escape, slowing an enemy for chasing down! - AWESOME ABILITY!

Bullet Time is a beast ulti but is to escape from however! You have to use this at the right time and preferably in a team fight or when you know it can completely turn a fight around for you! Or if you just REALLY want an easy gank hehehehehehehehehehehehehehe.

I love playing MF with a good Alistar, when you have that Infinity Edge you can set up some good ganks in a lane, if you can get the enemy out in the open you'll jsut drop them like it's HAWT! Other characters that are good to lane with are generally people with slows, snares or stuns... for obvious reasons really.

Early game, you need to hang back and harrass like a mutha' ****a' Impure Shots passive will doo all the work for you, plus it will help you to get them delicious last hits on creeps.

Mid game you should be doing a considerable amount of damage whilst being rather fast thus giving you the ability to roam for ganks in order to be a beast late game!

Late game is where it's at for this biatch cause you're guna be a mutha' ****in' ranged carry which means you'll be droppin' hoes like they're hawt.

I always lane with a friend of mine who goes by the name of NecroNetwork (http://www.mobafire.com/profile/necronetwork-67600) this makes it extremely easy to set up ganks and kills and to help each other get out, we use Skype every time we play to have full communication! i would suggest that everyone else have atleast one friend who they play well with!

Summary, Miss Fortune is a beast! simple as, just remember to use double up though, i tend to forget some times lolz (noob).
but if you just get some practise in with this build you'll just smash it up everytime!
GL&HF!

Grokaash
kbbz baaaaiii XoXoXoXoX *mwah*