Tristana

Bottom

Super Rapid Fire

Lane phase trade sustain, lane safety, and scaling

Precision

Improved attacks and sustained damage

Fleet Footwork

Attacking and moving builds energy stacks. At 100 stacks, your next attack heals you and grants increased MS.
Overheal

Excess healing on you becomes a shield.
Legend: Alacrity

Takedowns on enemies grant permanent Attack Speed.
Cut Down

Deal more damage to champion with more maximum health than you.

Sorcery

9% attack speed, 10 ability power or 6 attack damage

Absolute Focus

While above 70% health, gain up to +40 Ability Power or +28 Attack Damage (based on level), Adaptive.
Gathering Storm

Gain increasing amounts of AD or AP, Adaptive over the course of the game.

WhyFleet Footwork

As a heavy Crit stacking AD Carry, Fleet Footwork is a fantastic rune choice on Trist as it allows you to sufficiently sustain in lane and reposition with the burst of Movement Speed.

WhyOverheal

Overheal pairs nicely with Fleet Footwork and Taste of Blood, allowing you to take short trades and come out ahead thanks to the extra bit of health going in.

If you think you're going to have a hard time staying at full HP thanks to enemy poke, take Triumph instead.

WhyLegend: Alacrity

Tristana is all about getting in as many auto attacks as quickly as she can. Early game this means a quicker [E] stack and late game is means more crits.

WhyCut Down

As an AD Carry Cut Down is the most reliable source of damage amp as most other champions in the game will have more health than you do.

WhyAbsolute Focus

Absolute Focus on Tristana will provide you with a ton of Attack Damage when you stay above 70% HP. This should be relatively easy to do with your long attack range and Life Steal from Fleet Footwork, Bloodline, and items.

WhyGathering Storm

Gathering Storm is your late game insurance policy, making you a 30min+ game monster.