I've played Trist top before, and I can say...while I wouldn't take her top competitively, she's fun to use there. As long as you know how to poke and kite, Melee champs shouldn't be a problem for you. That being said, her only real niche there is going Hybrid: still enough AD and AS to be a relevant Marksman and Assassin for late game, but enough AP that she's not completely destroyed by Armor-equipped units.
I would normally always choose and max E first whether you're taking her AD, AP, or Hybrid. If you're against threats that can CC you from a distance (Yorick or Blitzcrank), then you should pay attention to their ability they pick first; at that point, it's really a choice between W for safety or E for waveclear. I would always pick W second and Q third, then max Q second and W third (like Trist normally does).
Word of warning: always be wary of ganks, and always save your Ult until the following two circumstances if you are ganked. 1) Your opponent is low. Kill the target with your ult, and this will cause your W to reset its cooldown (if it's still counting). Save your W until they start to attack you with abilities, and make sure that you can safely reach your tower (if you can't without using it, it just means you'll have to maneuver through any skillshots the rest of the way. 2) You're being chased by multiple champions. If they are grouped close enough together and you're too far from the tower or your W is on cooldown, Ult on one of them; while it's a single-target ability (and only damages the targeted unit), the knockback is AoE. If they're not close enough together, Ult on the most problematic one. If you're going to die even with these two circumstances, save your Ult as a possible Revenge Tool.
Summoner abilities...I normally take either Heal/Flash or Teleport/Flash. Heal makes your Laning Phase safer, and makes escaping ganks slightly easier, while Teleport is great for surprise ganks. As a Reset Carry AND Marksman Assassin, her ganks when done right are deadly and she can easily rack up enough kills when working well with allies to place her in an advantage against her opponent back top.
Like in bot lane, don't underestimate your opponent. Tristana can die very quickly when she makes exploitable mistakes, and without her W she's extremely weak to all-ins and ganks. Her E's damage, as well as the increased damage on her W from her E, depends on how many charges she can place on her target with her attacks (which is why her champion passive is so strong with her kit); you can use the lane pressure from this to your advantage to deny your opponent some needed farm, but don't push your luck and always keep an eye out.
