Why, hello. Welcome to my Miss Fortune ADC Guide.
Let me just give a quick runthrough of Miss Fortune here..

MF is an AD carry champion more suited to Bottom/Mid lane. Her skills are well balanced, and her Q Skill is good for harassing early game. As with all Champions, she has her pros and cons which will be discussed below.

Pros:
Good Harass Skills
Can slow enemies well with E
Ulti has rather long range
Has extra magic damage (passively)

Cons:
Slightly squishy early game
Success highly dependent on enemy champ

Starter:

Doran's Blade is a good starting item for Miss Fortune. The 5hp Lifesteal and 80 health helps Miss Fortune tremendously early game. This is recommended for most games.

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Long Sword and 2 Health Potions should be bought when looking to save money (by rushing the Long Sword to a Vampiric Scepter). This build, although saves money, should only be bought if you are confident of succeeding with Miss Fortune. It is a rather gutsy start.



Early Game Items:



Bilgewater Cutlass should be bought as the next item as it can be built into Blade of the Ruined King and gives Miss Fortune an insane advantage early game. Recently, the Blade of the Ruined King was buffed so it is the first main item to get. It also gives Miss Fortune early Life Steal for survivability.


Boots of speed should be bought after Bilgewater Cutlass. There is no need to rush this into Berserker's Greaves early, as the Blade of the Ruined King provides +40% Attack Speed.


This item is the first important item you acquire with Miss Fortune. With the Attack speed, life steal, AD, Passive and slowing active, it is massively OP. It is also built from cheap items that could help early game, making it good as the first item.


After Blade of the Ruined King, quicky upgrade your boots for 550 gold. This gives you a total of +60% attack speed at this point of the game, helping you out in farming.


Core Items:



Bloodthirster is important for almost all ADCs, including Miss Fortune. Once you acquire the Bloodthirster, you have a total of +95 additional AD and +27% Life steal. This, coupled with your attack speed makes you ridiculously powerful at this point.

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Statikk Shiv and Infinity Edge are the next 2 items you should buy in normal situations. Statikk Shiv's passive gives you some power towards the later game where ADCs start to stop shining. It also gives you 20% Crit, and 40% attack speed, bringing your AS to 100% at this point. After Statikk Shiv, Infinity Edge helps to amplify its effects by adding Critical Rate and damage. Infinity Edge also gives 70 AD. By this point, you should have a total of +165 additional AD.
Phantom Dancer should only be bought if the entire enemy team is feeding you and you have no threatening enemies. Each of these 3 items amplify each other, and after the 3 items you should have +150% AS, +75% Crit Rate and 250% Crit Damage. If you do not buy Phantom Dancer, replace it with the Tank Item that will be discussed later.


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Last Whisper + Phantom Dancer is a lethal combination against high armor enemies. Buy this set of items if you have enemies tanking with armor.



Tank Item:
This item comes down to preference.



Frozen Mallet gives +700HP, 30AD and allows basic attacks to slow enemies down.


Warmog Armor gives +1000HP and 1% MaxHP Regen per 5 seconds.


Guardian Angel provides 50 Armor, 30 Magic Resist and revives champion upon death.

PassiveMiss Fortune's Passive called Strut gives her Movement speed when out of combat for at least 5 secconds. After getting +25 movement speed, she gains 9 per second capping at +70 movement speed. Effect is lost upon being attacked/attacking. Strut allows her to have an advantage over other champs in movement, and at the start of the game negates the immediate need for Boots of Speed, allowing more focus on AD.

Q
Double Up is Miss Fortune's main attack skill. It fires a shot that bounces from one enemy to another one, and the second enemy gets hit with an additional 20% of damage. At max level, this skill gives 165 + (0.75*AD) damage. It is good for harassing and is your main skill that can deal your damage in early-mid game.

W
Impure Shots is another important skill for MF. It's passive gives Miss Fortune extra Magic Damage when hitting targets, and the Active allows Miss Fortune to quickly kill an enemy with low health or when killing Jungle Mobs.

E
Make it Rain helps Miss Fortune in many situations. She can support other teammates by slowing enemies and damaging them slightly using this skill, she can escape easily by combining Flash, Strut and this skill and she can slow enemies who are trying to escape to secure the kill. After slowing, Bullet Time can be used if the target's health is low. The slow secures a higher chance that the enemy will remain in Bullet Time's range.

R
Bullet Time is Miss Fortune's Ulti, and does significant damage to multiple enemies. It can be used to clear huge waves of minions, to bring an enemy's health to a low point, or to kill a vulnerable enemy target. It has a high range. However, later on in the game, it is really only used for picking off enemies with very little HP left as your regular attack will be giving you more DPS than this skill.

work in progress, guide will be updated