Miss Fortune ramps up speed with her passive Strut if she isn't attacked by an enemy unit. Avoid getting hit to keep her passive. This is an exceptional passive when it comes to reaching lanes quickly. Also, using this passive is a great way to close distances fast, such as crossing lanes to support or gank.
Use Double Up on the furthest enemy minion if enemy champions are hiding in back; it will bounce to them for lots of damage.
Double Up can hit enemies in bushes, even without vision. Use this is to your advantage by bouncing it off a visible minion/enemy champion, in the champion's vicinity.
Use Double Up on a tanky champion during teamfights and bounce it towards a squishy champion to maximize your damage output.
Use Impure Shots when facing opponents that have high health regeneration, or against anyone using a Health Potion. This will reduce their ability to heal and potentially get you an easier kill because of the effect.
Impure Shots is also extremely useful against a team or player with a healer.
Bullet Time is able to go through walls, use it to surprise tower-hugging enemies.
Bullet Time is a channeling ability, a stun or a silence can interrupt the ability so be sure that you are out of range to enemy champions with Crowd Control while casting Bullet Time so that it can not be interrupted.
Choosing Boots of Mobility will greatly increase her movement speed, but is only effective when roaming, since combat will reduce the Enhanced Movement 5 to 2. Plus, she is at risk of losing her Strut bonus as well.
Choosing Mercury's Treads will help her get out of trouble when focused with CC since she will have lost her Strut bonus.