Hi,
This guide will show you how to build AD Tristana properly, and basically how to get out of "elo hell". But a good build isn't enough to get out of elo hell, the thing you need to do that, is to use your brain and your skill. I say this because i see too much players playing stupidly and badly. I'll try to teach you how to do this in this guide.
Leave me a comment vith what you think about this builde and the guide in general.
Oh by the way i'm french that's why i make so much english mistakes ;)
And this is my first ever guide, don't be rude :p

The runes i used here are pretty basics:
I pick Greater Quintessence of Attack Damage ( 2.25 x 3 = 6.75 AD ). This will help you a lot early game, to last hit easily and to harrass a bit your opponent. But sadly this isn't that usefull late game.

I use Greater Seal of Armor ( 1.41 x 9 = 12.69 armor ). That small boost of armor will be usefull in early/mid game. Obviously you're going to lane against an ad carry and a support. These runes help you "survive" from your opponent's potential harrassment. However there a bit less usefull when it comes to lategame. But imo the main role of runes is to help you early game, you have to make the difference in early game, and these runes will help you do it.

For glyphes, i chose Greater Glyph of Scaling Magic Resist ( 0.15 x 18 x 9 = 24.3 magic resist lvl 18 ). Basically we need a bit of magic resis to stay alive long enough to kill ennemies, but the things is that you're gonna fight against AP carries from mid game to the ened of the game, but not before. That's why magic resis per level is good, because in your lane you're not gonna face that much magic damages, except if they have an offensive support such as Zilean.

Finally i have Greater Mark of Desolation ( 1.66 x 9 = 14.94 Armor pen.). These runes are really great, they're gonna be really usefull when your ennemies will buy armor. These runes will be usefull from the beginning to the end of the game. In late game, having these runes is better then having AD runes.

Not that much to say there. 21/0/9 pretty classic for an AD carry. Swiftness will help you catch/escape ennemies, Runic Affinity is great for longer red buff, and finally Vampirism will help you sustain is the lane.

Here comes the big part of the guide.
I start with a Doran's Blade , which is pretty basic. Coupled with Vampirism , you'll have 6% lifesteal which is pretty good to sustain well in lane. The health will really be usefull to do not get raped by your opponent, and finally the extra damage will help you a lot in last hitting/harrassing.
You can buy up to 3 Doran's Blade, depending on how much money you have when you go back. Basically is you have 1650+, go for B. F. Sword and boots if you have enough money. BTW the next item to buy are Boots but if you have enough just get B. F. Sword. This item is really important because it will increase your damages a lot and you'll start to deal significiant damages on champions, and you'll be able to last hit really easily. If you have 975+ and already boots of sppeed] and [[doran's blade, you can buy Pickaxe, which will do the same as B. F. Sword.
Then just finish your Infinity Edge, but get bf sword and Pickaxe before Cloak of Agility, because at this time you'll still be laning and you have to farm, whereas critical strike is random and it won't help you farm.
After finishing your Infinity Edge, you should upgrade your boots of speed] to [[berzerker's graves.
Now you start dealing pretty decent damages, but it's still pretty random because you rely on critical strikes. The next item you have to buy is Zeal, and you have to buy brawler's glove first because as i said it, critical strike is our main source of damage.
Then buy Cloak of Agility to get really op. Zeal is a great item, not only because of the attack speed and the critical chance, but the movement speed will really help you, because the main thing you have to care about is your placement in teamfights, and your focus of course. IMO at this time, if you farmed well, got atleast two kills and didn't die too much, you start to deal crazy damage.
Then just finish your Phantom Dancer, and buy a Vampiric Scepter, this will help you survive and also you'll be able to stay longer without recalling because you'll heal yourself for a pretty good value.
At this points , you have two choices :
if everything is going well, you get kills, they do not kill you, just finish Bloodthirster.
The second option, is if you get killed in teamfights before dealing damages, and if they focus you a lot. In this case you have to start building a defensive item. IMO the good defensive items on Tristana are : Frozen Mallet , this is the main defensive item i would recommend here, because it gives you a lot of health, and also a bit of damage, but the passive is really intersting here. This passive will make you (almost) impossible to escape, and hard to chase.
The second defensive item you can get is Banshee's Veil. The health and the mana are pretty good, and the magic resis. too. I recommend you to take this item if the ennemy AP carries deal crazy damages, or if they have a stun (a champ like Sion , Taric...) or a lot of cc ( Blitzcrank, Alistar...)or an engage spell ( Amumu's Curse of the Sad Mummy, or Nunu & Willump's ultimate zero). The shield you get from this item will save you many times, but it can also be wasted on a small spell. That's why this item is really random and risky.
The last defensive item you can get is quicksilver's slash, this is an improved Banshee's Veil, but without the health/mana. Again , take this if they have a lot of CC.
Then get the bloddthirster if you got the defensive item, or get the defensive item if you think it's needed.
The final item will be Last Whisper if they have builded armor. Remember that armor pentration is great at this time, because having 40% armor penetration can be more than 100 damage on a tanky ennemy, so think about this item instead of only damages !

As you have seen, i level up Rocket Jump, because this skill is jsut an incredibel escaping/chasing tool, than i take a level in Explosive Shot, and finally i max Rapid Fire pretty soon. At level 5, u'll get +90% attack speed, which is great even if you do'nt ahve that much items.
WE can say that the skill sequence is R > A > Z > E .
Don't forget to use Explosive Shoton champions like Vladimir, or Fiddlesticks when he uses his Bountiful Harvest, because it will reduce healing by two. You can also use it on a champion who uses Heal.
Don't waste your Rocket Jump, wait until you need it to use it.
Your ultimate, Buster Shot should be used like Vayne's comdemn, you need to stick an ennemy to a wall with it, even if it deals decent damages.

Pretty basic summoner spells. Exhaust is always good on an ad carry, and Flashcoupled with Rocket Jump can be really OP is used well.
Ignite can be taken because coupled with Explosive Shot it will deal nice DoT.
Finally you can use Ghost instead of Flash to cahse/escape ennemies faster.
Also, you can use Heal, it's a crazy baiting tool, and with your jump shot + burst shot, you can surprise ennemies after baiting them.

IF you see the ennemy AD carry is quiet low HP, and you have mana and your ultimate, you can Rocket Jump behind or next to the ennemy to use burst shot to comdemn him in a wall, if used well, it will hurt considerably and stun him.
And don't forget, when you kill or get an assist, Rocket Jump's cooldown resets. That mean you can towerdive with it and go back with it really fast and take only one turret hit. Also, dont' forget that Explosive Shot deals DoT, which means iif you use it on an ennemy, you will get attacked by the ennemy touret if you're in range, so be careful.

So here it is, i hope you enjoyed my guide. Using this guide, i have had over 90% wins in ranked, and now i have around 80% (Check yDDEH on EUWif you don't believe me ;) ), i already got a pentakill using that build too.
Tell me if you enjoyed my guide and leave a rating. If you downvote it, tell me why :)
See you in game ;)