Miss Fortune can be played any number of ways. My preferred method is to use her speed to destroy her opponents before they have a chance to lay any hands on her. While others may disagree with this build, I have found that 9 out of 10 games, I get an early kill lead and maintain this throughout the end.

Since MF can be an early game Mana hog, I like to use the clarity as much as possible to keep her abilities available. Make It Rain is one of her best abilities, doing a nice amount of damage (even without AP) and slowing them down. The only one better is her Impure Shots. Since this build is all about speed, you could have an end game attack speed of about 3.0

Teleport is MF's best friend. She should be focused on towers, both saving them and taking them out.

Don't rely on her Ult to make those kills. It's a good back up, but with her speed and crit, MF's auto attack is SO much more destructive. Use it in team fights for multiple targets or even to clear those minion waves to push a tower or get them off yours (if there's a Champion hitting on it, as well)

When starting game, buy your basic Boots and three Health Potion. The play style here is very important. If you are playing mid lane, you must keep the heat on the opposing champion. Stay behind your minions, last hitting for the gold and popping a shot at your enemy champion when ever possible (and this should be often). The reason for this is to keep yourself safe from most early game attacks and to keep their life low. Let them burn through their Health Potion and Heal. Focus your Make It Rains to hit minions and include the Champion on the edge of the AOE.

If at any point the opposing Champion wants to go toe to toe, let them. Make sure you are at least level 3 (giving you both your Double Up and Impure Shot) Due to your massive early game speed, and Double Up resetting your auto attack, you should be able to clean up that kill. Following, use your Health Potion or return to base to heal and purchase those boots.

If you haven't managed to kill your opponent, yet, wait till level 6. Your ult makes a great harasser to push those minions, pick up a kill, or just hurt them enough to return to base, allowing you time to put a dent in their tower. At level 6, you'll have enough to get your Greaves (if you don't have them already) as well as the Vampiric Septer. If you don't have Teleport available anymore, as long as you managed to push that wave back, then you will have enough time to return to tower before any damage can be done to it.

At this point, you may have a couple kills in mid, or none at all. Just keep farming those minions, harassing your opponent enough to return to base to heal, and take out that tower. Keep it up till the tower is gone. You should (and better have) enough gold from last hitting minions to start if not finish your Bloodthirster. This is where the battle changes.

Once that tower is cleared, begin your ganking. Simple. Choose a lane, hide in the bushes and gank the hell out of them. If you kill them or not, you should be able to help that duo push their tower. Always keep your eyes on the mini map. If you need to clear some minions or a Champion that got ballsy enough to hit your mid tower, Teleport back and chase them off. Keep up your build, and pay attention to your gold. You should be able to quickly purchase your Black Cleaver, giving you a great boost to your speed, attack and make those tanks just THAT much squishier.

At this point in the game, it's difficult to tell you where to be. Help your team push towers, but stick to the back of the fights. If a team battle emerges, do what you can to help, but keep your eye on their unguarded tower, as well. MF can easily melt a tower at this point with a couple friendly minions, and her speed from her build as well as her Impure Shots.

Once you've helped push the first of the lane towers, you're job has only started. At this point, you're build should be nearly finished. The last two items are optional, and should be based solely on how the game is going, and what champions you are facing. The second Phantom Dancer can be easily swapped out for a Last Whisper if tanks are too troublesome, or a Madred's Bloodrazor. The Infinity Edge, while sometimes the best option, can also be swapped out for a Trinity Force. Again, these are all optional and should be chosen depending on the Meta-Game.

Team fights should be erupting everywhere at this point in the game. Swap between helping slaughter them, and taking out towers. My best strategy is to help the team fights (staying near the back and dropping your Make it Rain to slow them down), and then when a large wave of minions is near a tower, Teleport in and wipe it out. If you've managed to take one tower, and enough enemies are distracted, you might be able to take two. Use Make it Rain and your Ult to quickly clear minions to allow yours to hit that tower. If a Champion appears, take them if you can, or run and fight another day.

MF can be quite a beast in team battles, but her best advantage in a game is to clear those towers. Keep that in mind at all times.

Bloodthirster works best when fully loaded with kills. If you die, jungle and farm a little bit, get that red buff, and make sure you're ready to face off again before charging into battle.

When finished with a kill, don't fret over low life. DO NOT return to base unless you are going to purchase something. Kill two or three minions or monsters and you should be back up to snuff due to your health steal from your Bloodthirster.

Keep one eye on that mini map. You might be able to take a tower, save a tower, or gank an enemy that pushed past your minions to chase a team mate.

MF has a ridiculous potential for dealing massive amounts of damage quickly through just her auto attack, alone. Rely on her Impure Shots and Make It Rain to take out champions quickly and keep them within shot.