Hi m8s, it's my first build here, at mobafire.com. I wanna to tell u how to play Miss Fortune, my favorite carry champion at mid lane. Also I want to tell u something about this girl, I'd never lost mid lane first as MF.

Marks of Desolation - I hope u know it.. we'll play full AD MF with high attack speed.
Seals of Vitality - HP it's important. Why? better lane control and help u in duel 1on1 if enemy rush u.
Glyph of Focus - Ulti cooldown reduced. You'll easy dominating at ur line

Ok now items.
Dorans Blade first. Why? more hp, attack dmg for easier last hitt
Berserker's Greaves Don't try to get another boots. Attack speed req.
Dorans Blade one more time if u have problems.
Now we need to buy Bloodthirster If u have it u'll easy finally push mid. this life steal + life steal from dorans make u very hard to kill in 1on1 duels.
Phantom Dancer more more more attack speed, movement speed and crit chance. This item must be at every MF.
The Black Cleaver & Madred's Bloodrazor imba attack speed boost, armor reduction, %hp per hit, and imba dmg boost.
Last item i buy is Infinity Edge Crit dmg, crit chance, dmg all u need
If u have it all u can try to sell ur boots and buy one more phantom dancer 100% crit chance and more attack speed

I told u to take W skill first.. It helps you in farm minions. Try to only LAST HIT minions until lvl 6.
Q max first. Harass ur enemy every time he is in range. Remember to hit minion with this skill becouse player behind him will get more dmg ;)
E.. add at lvl 5 only for slow. we dont need this skill to do dmg.
R finally lvl 6. Try to spam ur ulti all time to killing waves of creeps u will farm well, harass, and then u can hit turret. In Team Fights important thing is. Use E first at ur enemies then nuke them with R.

Flash and Exhaust
Flash - Can help u to finish enemy, leave team fight if u are to close or just escape
Exhaust - If u have boots, 2x doran, and bf sword and ofc some hp, u can easy go in enemy and nuke him using this skill :)

It's all i can tell u in my poor english. I hope u understood something;)

Enjoy!