Why should you play Miss Fortune
In a Nutshell:
Very big damage, pretty safe laning phase, high mobility
Description
Miss Fortune has very high damage with new actual lethality items, allowing her to melt the whole enemy team in seconds. Just take a good position use E > R and the job is done. The laning phase is pretty strong too, because of her long range, slow on E, and great poke damage.
Runes
Main Path:
Press the attack is a pretty good option on Miss Fortune because of her fast trades with AA Q AA.
Triumph is the best choice because 2 other runes are pointless on Miss Fortune.
Legend: Alacrity gives her the AS that she needs.
Coup the Grace makes one shotting targets easier.
Secondary Path:
Absolute Focus helps with bonus damage at traps, which you like to make.
Scorch boosts trades at the laning phase.
Summoner spells
Ghost gives option to chase someone, or change position faster.
Items
If the enemy botlane has long-range poke, you can take Doran's shield eventually.
Early Game:
In the early game, you need to be careful and don't engage in enemies. Just focus on farming and poking with your Q. Save your E to slow the enemy when they want to engage you and run away. If you outpoke the enemy- now you can engage, go for kills, and reset for items, you want to safely snowball to 2-3 items.
Midgame/Lategame:
You want to use your ultimate by surprise, just stay near your team, and look for opportunities. If you don't have ultimate, or can't run around for ambush, don't run in the enemy, you are very squishy, and you don't want to get oneshoted. Stay on long-range, poke with passive and Q, run back, and repeat.