this is the way i play tristana and i win a lot of matches.
hope you like it!!!

Tristana is an awesome Champion for a lot of reasons
1)Passive gives much attack range which at late game is awesome
2)''Q'' Ability at level 5 gives 90% attack speed
3)Has the biggest escape ability in game(i think)
4)Can save your team by ultiing an enemy champion ready to get a kill
these are some of the reasons

the basic runes for an Ad Carry
10 Attack Damage
10 Armor Pentetration
10+ Armor
10+ Magic Resist
perfect setup which can save you and dominate in early game

these are the masteries i use.
the normal 21 on attack tree
8 in deffence for health+armor+magic resist
1 in utility for the flash cooldown(even if you have ''W''

start with Dorans Blade
at your first trip back buy Boots and 2nd Dorans Blade(ofc when you can some Health Pots-Wards)
then finish boots and purchase another Dagger so you can finish Zeal ASAP,then buy Saphire Crystal for Sheen and then finish Trinity Force which provides everything,just everything.Then Scepter-ofc you can buy Lantern if you want but i would suggest go straight for Bloodthirster-into Bloodthirster.Then Start and Finish Infinity Edge and have fun!Then you can buy armor-magic resist items or Last Whisper(late game sell the double Dorans)

Your ''E'' provides awesome early game cauze of his passive that explodes on death.Also you can harrass a lot with it's active.Maxxing ''E'' 1st is awesome for chasing-farming-escaping.''Q'' is only nice for late game turret pushes or team fights so thats why max it last.Level Up ''R'' when possible

Flash for escape-chase
Exhaust for escape-chase-1 vs 1(cause of attack speed reduction)

otherwise,Cleanse if they have heavy AP team

I Really hope i helped you out.
i think this is a good guide for begginerss.
Let me know what you think