Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
You want to focus a lot on the attack speed when building this build, then on the attack damage later on.
Helpful fighting tips:
When fighting, use the range that is so kindly given to you by Tristina's special passive skill to your advantage. In mid game if your opponent is standing by their tower trying to take out minions, you can usually hit them and be out of the range of the tower. if they move behind the tower hit the tower if they are in front move back and hit them.
Try to stay in your lane as long as possible.
And STAY BACK! you are very squishy so you can't take a lot of damage.
Magnificent escape mechanism.
Cool combo: use rocket jump to jump over your opponent and use buster shot to shoot them towards your tower.
You want to level up explosive shot first because when you last hit minions they explode dealing damage to all who are close, this will give you more minion kill = more money and if a champ is near them you get free damage on them. Also you can harass with this skill by using it and running back behind minion line.
I get rocket jump for the escape/ chase mechanisms. I find 1 skill is good enough seeing as I don't really use it as an offensive ability.
Then I max Rapid Fire to snipe towers or champs.
GL, HF, GG.
Please comment if you want a more in-depth description.