One of my favourite ADCs, though admittedly with a weakness when it comes to her lack of crowd-control. Still, hearts stream out of her arse, boosting her movement speed greatly, and nowadays her ult deals Physical damage, what's not to like? :D
- When she was first released, Double-Up used to be the end-all of abilities; a great physical-damage nuke with an even greater nuke to the target behind. It has since been nerfed and I don't see it being regarded much these days, but let's try to bring it back, huh? It's actually still pretty good. I advise incorperating a Tear into your build to make using your Q mana-efficient; since Manamune now deals Physical damage, this approach isn't so obscure in the long run.
- Use Double-Up to zone your lane opponents; they'll either have to hang pretty far back, or get ahead of their minions to avoid the damage. If you've made your Q mana-efficient (or you have a Soraka), it's uncanny. If you don't have a Tear or a Soraka, then you should make sure to use it only if you have more than half of your mana. This will make sure that in a dire situation, you can use all of your abilities.
- Try smart-casting your Q. It'll make life a lot easier as it has your auto-attack range, so whilst you're right-clicking an opponent, you can also tap Q for extra damage. Note that Double-Up does not utilise your auto-attack, and deals base damage + your total AD, meaning you're effectively landing three attacks in a single moment. If it's smart-casted, you won't lose any time in doing so. Did I mention that it also deals On-Hit damage? Feel free to experiment with a Sheen, and be amazed at the results.
- When ulting to finish a wounded target, be sure to get as close as safely possible to extend the range should they be retreating. Also try to aim the cone so that it encompasses where they are and where their retreat-zone is; perhaps if you're not going to kill them you can at least make them run the wrong way.
-Remember to use your W's active on high-regen or healing targets such as Dr Mundo and Singed. It's easy to forget in the heat of the moment, but cutting 50% off their healing will cripple them, and your teammates will be ever so thankful you did it.
- It's unfortunately easy to focus Miss Fortune as she doesn't really have an effective escape tool; her passive is disabled upon taking damage. Try to keep a safe distance in fights, and anticipate gap-closer assassins such as Akali; make them work to reach you, use Make It Rain wisely, and if need be, purchase a Guardian Angel.
- Combine your ultimate with crowd-control intensive champions such as Amumu or Jarvan IV; if you can dish out the full serving of damage to the enemy team, you'll have done your job more than effectively.
Hope that helps any Miss Fortune players - just remember that your Q (especially when smartcasted) greatly increases your damage output when autoattacking, on-hit effects inclusive. It can also help you land a last-hit on a fleeing champion; often in bottom lane you'll have a situation where you almost killed their ADC, who is now out-of-range with their support trying to take the bullets for them. Let them! Double-Up the support, and (I've had this happen shockingly often) the ricochet will kill the ADC! :-)
All the best. :-)