So we have all seen the Tristanas that do amazing in game, or very terrible. Sometimes they start off great and then end up as feeders. In this guide, this is how I build and it works great for me. Again , this is how I build her. You may do it differently. But often, I can easily carry a game out.

Some Pros and cons of her are:
Pros
High damage
Slow
DoT
Easy escape
Carry

Cons
Extremely squishy

So as Tristana, you will want to stay at range. ALWAYS TRY AND GET MID. <---- Important. Tristana is a great mid. Depending on who you are facing, you should be able to own most mids. The ones that bring trouble are Mordekaiser and Vlad. For these, you will want to just stay back and not get hit; Also call in ganks on them. Do not be afraid to leave your lane to gank. Tristana is a amazing ganker with ghost and ignite. You just hop onto them, they get slowed, use your stuff and they should be almost dead. One thing that is SUPER important, always jump in FRONT of them. This way you can knock them back. Unless you are positive you can kill them with it, save it. You can always try again.

The reason I use armor pen runes, is because generally the opponent will start to stack armor against Tristana. With this, late game they will be able to kill you. That is why you get armor pen. Plus you will hit harder.

The greater seal of claritys allow you to keep harassing longer. One thing that is awesome about tristana , is you have a long range, and you can use your explosive shot to hit them, and over time it will still do damage.

The magic penetration is just for your w and r really. You can substitute these runes for numerous other ones. It is just my personal preference.

The fortitude ones I strongly suggest , at least for a new Tristana. 75 bonus health on her + a dorans sheild sets her health above most mids. Usually you can kill them once or twice before you even have to leave the lane because of these bad boys.

I start off with a Dorans shield to set my health up against most mids. This way, you will most likely get first blood. From their it is easy pickings, you can also go get boots if you want.

Right now should be your first time going back and you should have 1k-1.5k gold. Get berserekers greaves. Maybe an elixir if you really want it. (I dont understand why people dont use these more often, they cost 250g, which you can get back easily, and your health will be very high). Then go back to your lane.

Now is your second time coming back, you should have been ganking so you should have 2-2.5k gold. Get a bf sword.

Your 3rd time going back should be when you have enough for infinity edge. This item will boost your damage up more than any other item. Super good item.

If you are getting killed or focused, you may or may not want to rush a Banshees veil. This or a phantom dancer. You will be moving much more fast and attacking a lot faster.

If you didnt get banshees veil, get it now. This item is important to her. Late game she is a glass cannon and will get focused. If you really want to you can substitute a Guardians Angel for it, but I like this better. Any good tank should be keeping you free of champions anyway. And if they get you, your Banshees blocked it.

Grab your bloodthirster and your damage will be insane. Paired with your other damage items, you should be hitting way hard and you'll be stealing life. You should be able to 1v1 the carries and the supports. Do not try to take on a tank unless you get a black cleaver instead. Even then, I do not support getting a Black Cleaver over a bloodthirster. At late game, depending on what they have and if they are tanky, you will want to sell your dorans for a Black Cleaver, if they arent tanky, you can substitute it with a Phantom Dancer..Another bloodthirster..whatever you choose.

Solo Mid
In your lane, you will just want to keep harassing with your e until they are half health. Once this is done, use your w and go kill them! Pop an ignite if you need to, explosive shot and ignite together are deadly. Use your ult if you have to as well.

1v1
In a 1v1, if you do not initiate and dont think you will win, dont risk it. You'll be worth a lot of gold. If you initiate or you think you can kill them, pop your q, then w onto them, then use e and ignite. Use R to push them back. Then AA away.

Team fight
Team fights are scary for Tristana, you should be behind everyone in a team fight. Do not EVER be in front. Do not face check the bushes. Stay by your tank. he is there to protect you. If your tank dies and they are winning the team fight, try to get out of there before you are aced. You will die extremely fast. Just because you raped them early game does not mean you can be as cocky late game. This will feed them and you will get weak.

So there is the guide, it is my first. Tristana is one of my favorites. Feel free to change up the build a little bit. No build is the same for every team. If they are tanky, get a black cleaver. If they have lots of meelee, get a Frozen mallet. You understand. If you don't, delete your account and start new. You have obviously missed something.

Tristana is a amazing farmer. Her e does explosive damage, dont forget this. If there is a huge snowball of minions, w on top of them, AA one of the minions till it explodes killing 4 other ones. Repeat. Extremely effective :)

Dont get cocky, you will die.
Dont go off alone late game, you will die.
Dont rage at your teammates, they are at least dummies while you kill the other team.