Her E and Q makes taking down turrets a piece of cake. Avoid letting her get free shots on your turret since the tower platings will give her a gold advantage over you.
Avoid extended trades with Tristana whenever her E is on you. The more auto-attacks she hits you with- the more damage you will take.
Tristana will often use her W aggressively. If you’re strong and have good all-in, you could try to trade back with her and use her mispositioning to kill her. Take a quick glance at the minimap to see if her Jungler is nearby before committing to the fight though.
If Tristana uses her W aggressively, burst her down or CC her so she is unable to reposition and clean up the fight. Taking her down early will make it really difficult for her team to win the fight.
In the mid-game, if Tristana is ahead, avoid walking too far forward if you’re alone. She has great all-in and pick thanks to her W and E. Keep at an appropriate distance away from her so she cannot easily take you down.
Tristana has a lot of self peel with her W and Ultimate R. To make fighting easier, try to play around her Ultimate R or look to flank her in team fights. This will make it harder for her to kite/escape the fight.
The longer the game goes and the more gold Tristana has, the stronger she will be. Reduce her chances of carrying by putting her behind in the early game.
In the right matchup and with an all-in Support, Tristana is really strong at level 2 or 3 when she has her W and may look for an early kill.
Once Tristana has completed her first item, she will be much stronger and able to trade more effectively. Do not overextend or push too far up in lane if she has the item advantage.