Miss Fortune is one of the best carries in the game. I prefer to go mid or solo lane with her because minion farming is her life. As with any ranged carry, the more minion kills you have the more successful you shall be. However she can be successful during laning if she goes with someone who doesn't need the minion farm such as a support character like Taric or Sona.

Flash is a must in my mind, especially when going mid land or solo lane. The anti-gank power of flash against enemy junglers or just any gank in general. Flash is also particularly helpful for team fights when you find yourself to far into the fight and need to position your self for a Bullet Time.
Ignite is a good spell in my mind just for the early kills. Its not hard to get early kills with Miss Fortune if you harass well with Double Up.

Double Up, Double Up. Get it first because of the harass capability and minion farming use. Not to mention the low mana cost compared to Make it Rain. Max it by level nine and you should be golden. It also applies on hit effects just in case you buy a frozen mallet as a situational item.
I get a rank of Impure Shots at level 2 for the minion farming aspect of the game that is so important for Miss Fortune. 6 damage might not seem like much on a last it but it does help and in case you're doing an abnormally good job of pushing the turret the attack speed bonus gained on activation is a helpful addition.
At level 4 the rank of Make it Rain is important for the anti push capability. I caution against using this in rapid succession because of the relatively major mana cost compared to double up especially when you're using it simply for harass.

Start with a Meki Pendant and a pair of health potions. Meki pendant is great for ability spamming and makes it pretty near impossible to run out of mana if Double Up is the only spell you're using. The Health pots of obvious reasons.
Next I take Berserker's Greaves. I take them because she doesn't need swiftness with her passive Strut.
Turn the Meki Pendant into a Tear of the Goddess and mana problems are officially forever gone.
Next the Zeal. The attack speed and crit on this item makes minion farming a breeze hopefully you're pretty well minion farmed at this point, but don't stop. I only get part of the Phantom Dancer because having small amounts of damage on a carry is counter productive.
That's why Bloodthirster comes next. I take it early because it's possible that farming is still occurring and stacking the minion kills on Bloodthirster is an absolute must. Not to mention the survivability that comes with the Lifesteal gained.
Now finish that Phantom Dancer. Now is when you start to understand the damage of Miss Fortune. The critical chance upgrade leads into the next logical item.
The Infinity Edge 250 percent crit damage? Talk about item synergy. Also damage greater than an unfarmed Bloodthirster and extra crit chance make this a must for the next item.
At this point you have many options my favorite being another Phantom Dancer. Now you're nearing 100 percent critical chance and you're attack speed is really starting to grow and therefore your damage output.
Since there's nothing left to do finish the Manamune. Miss Fortune has a decent amount of mana by the end and the increasing amount as you stack this is helpful. Although as I will discuss later this is the first item i would take out to get situational items.

First one I can instantly see being viable is a Frozen Mallet. This is an effective item choice against teams that have that annoying nuke mage that focuses you down early in team fights.
Next A good item in certain situations is the Banshee's Veil. Good choice for teams with a snare or long ranged support character's harass spells.
On a unbalanced mage team buy a Quicksilver Sash. The active is helpful for escaping snares and especially ammumu's ultimate. Rarely is this the way to go but just in case.
Another potential item against big health teams is the Madred's Bloodrazor. Not always a good way to go because you sometimes reduce all around damage on the squishies, but its invaluable for teams with characters such as Olaf, Vladimir, and most tanks that have Warmog's in their core builds.

Stay in the Back. Period. Miss Fortune, especially with the build specified is a very very very squishy character. Staying behind the tank is an absolute must or you will die and you will die very quickly. Positioning is key to being successful. One thing I find helpful is taking Flash in case you do over commit yourself. Flashing out and then letting loose a Bullet Time is deadly indeed.
Don't initiate with your ultimate however, That's key also. People will be able to easily run out of its range and area of effect. Wait until the chaos of a team fight is fully in play and then let loose. Try to drop Make it Rain before your ultimate as well. The slow keeps them in the area of effect longer and gets you in a pretty good range area to maximize its full effectiveness.
After the ultimate you will probably know whose going to win the fight so either it's run your *** out of stay in and rape whatever is left of the main DPS characters of the other team. Some where when you think the battle is fully committed pop Impure Shots for the extra attack Speed.