Hello everyone, and welcome to my very first guide!! I've decided to make a guide for Tristana, the champion that took me to Gold 2 this season so far.
As someone who has terrible mechanics, and god awful positioning skills (and map awareness), Tristana's kit has blessed me with the answers.
She is by far one of the safest AD carries to play, with an ability to reposition herself, escape from ganks, and and ult that can be used defensively.

Early Game
Early game for any ADC is the same. Farming minions.
You should get at least 5/6 minions each wave, but it may be difficult due to Tristana's E passive. However, you can utilize this to pick up cs that you otherwise might have missed. Practicing controlling the wave and Csing will allow you to dominate your enemy with sheer farm numbers.
Trading
Trading with your E is an OK idea, but don't do it too often, as it will make you oom quickly.
Use your scaling attack range to trade, as it is Tristana's biggest advantages as she levels up.
Mid Game
This is when teamfights begin. By now you should have an infinity edge, and your attack speed item (or at least a zeal + other component). Tristana's range should be more significant now, and will allow you to stay in the backline and dish out damage constantly while staying safe. If you get caught out, your W - Jump can help you reposition.
REMEMBER. ATTACK DAMAGE CARRIES SHOULD ATTACK THE CLOSEST ENEMY TO THEM. DO NOT JUMP IN TO HIT THE OTHER ADC OR SOMEBODY ELSE. SUICIDING = BAD.