(Tristana got a good early and a way better Lategame)
If you are on the blue Side try to lead your support to the Golems and do them otherwise you help your jungler.
When the laning starts try to harras them with 1 autoattack and a E right after an back off. (110dmg E lvl 1 + autoattack)
If the Enemy Supporter got a heal and your doesnt try not to lose that much hp in these trades

Since Tristana is pushing automaticlly try to get the enemy tower early ( WARDS )
you get more range the higher your level is. You have Caitlys range with lvl 9-10. With Lifesteal and that range you can easily outharras them. Once you got the Bottower head to the Midtower and Dragon you have way more Pressure since the enemy bottower isnt there anymore.
If it comes to Dragon fights DON'T use your W as Damage spell just stay in Range

Tristana got one of the best lategames since she got 700+ Range and an incredible Attackspeedbuff (90%). Just try to stay in range. Search for a safe spot in teamfights or kite them.
Dont waste your Q for like 2 autoattacks.

I played Tristana from the middle of Season 2. I was silver there and i startet getting better and with alot of games with Ashe and Tristana i got platin at the end of Season 2 but i still get better and i am on my way to Diamond right now.
So good luck in soloQ i hope you learned something from that guide :D