Tristana is a unique AD carry (in my opinion anyway) in the sense that her skills can be used to burst like an AP early game while transitioning into a full AD carry with 703 range at level 18. Her rapid fire is also a very powerful AS steroid, stronger than most people's ultimates. Her rocket jump is a good escape or chasing move because it refreshes on kill or assist but as of right now there are a lot of things that can stop Tristana mid jump, making this skill sometimes frustrating to use.

Overall I think she is one of the best AD carries and it is definitely fun to watch Tristana goomba stomp your enemies if you keep refreshing rocket jump.

Greater Mark of Desolation Greater Mark of Desolation
and
Greater Quintessence of Desolation Greater Quintessence of Desolation
Armor penetration is useful throughout all stages of the game whereas flat AD falls out later in the game.

Greater Seal of Resilience
Tristana is squishy. The armor and magic res runes in addition to the health, armor and magic res from the defense tree help make her less squishy during laning.

Greater Seal of Clarity
Tristana's skills are fairly powerful during laning phase. Some people prefer the extra mana regen if they're a bit too spammy with their skills and that's perfectly fine.

Greater Seal of Shielding
I personally prefer scaling MR because early game you don't have to deal with AP as much. By mid game and when team fights start happening your shielding runes should have already scaled to be equal or better than warding runes

21/9/0

The summoner spell masteries were left out because you would only get them if you planned on taking said summoner spell. I chose not to take summoner's insight because veteran's scars is like having an extra health quint. It's all personal preference though. If you prefer to have flash cooldown 15 seconds faster or have teleport cast 1 second faster then that's up to you. I prefer 1.5% damage over 3% lifesteal, though both do not have a very significant effect on Tristana overall. I just hate seeing the enemy survive with like 10 hp.

Early Game

x3 Standard starting path for many characters in the game. The boots help you farm, avoid harass, chase etc while the pots give you lane sustain on top of what your support provides.

This will help you farm and will eventually be built into Infinity Edge. If you're losing your lane pick up 1-2 Doran's Blades before the B.F Sword for their cost efficiency to help you stay competitive with the enemy laner.

These are incredibly cheap for what they do. Extra movement speed and attack speed are always welcome. However, switch these out for mercury's treads if the enemy team has a lot of CC, hard or soft. Alternatively, you can build this first for the extra attack speed early game and sell them later in the game for mercury's treads once team fighting starts.

Mid Game

Good damage, extra crit chance, and extra crit damage from the unique passive. This synergizes very well with a phantom dancer, which you'll be building soon.

For 450 gold you get basically the same lifesteal as an unstacked bloodthirster. Definitely worth picking up early.

The extra attack speed and crit chance synergize with Infinity Edge quite nicely. The extra 15% movement speed is also a nice bonus for repositioning yourself, running, or chasing.

Enemies should not be ridiculously tanky at this point in the game, but you'll see some armor items starting to be built by now. If for whatever reason the enemy is already armor stacking at midgame then pick this up after building a zeal and finish your phantom dancer later. Only start building this if you notice armor popping up in the enemy team's inventories, else you can just go straight for your bloodthirster and come back later for this.

No armor? No problem. Build your bloodthirster first then come back and build a second phantom dancer. This puts you at 85% crit, gives you another 15% movement speed boost and 55% more AS. Only do this if the enemy team is not building armor, and will not in the near future for whatever reason.

End Game

Finish this up for some extra AD and lifesteal (build before last whisper and second phantom dancer if the enemy team is ignoring armor items for some reason). Remember to farm this up ASAP after you die to make it as cost efficient as possible.

Your nope.avi for all the enemy CC that gets thrown at you. Because this item is so cheap (cost wise) you can finish this anytime in the build whenever you need the cleanse effect. Even just building the negatron cloak and coming back to finish it can work wonders against the enemy APs.

Sometimes the enemy does not have much hard CC and thus the extra health and the banshee's bubble would probably be more useful to you. Adapt your build accordingly

Rocket jump first for the utility. Explosive shot next to help out with your early game burst. Add another point into rocket jump for more burst and lowered cooldown followed by 1 point into rapid fire. The AS boost at rank 1 is mediocre and can potentially help you repel a minion wave or get one last hit on the enemy before he walks out of range. Get one more point into rocket jump at 5 then pick up buster shot at 6 (obviously). After 6 start maxing rapid fire because you'll start having some AD items at this point and because you stop relying as much on your burst. After rapid fire is maxed take rocket jump and then finally explosive shot, upgrading buster shot whenever possible. Explosive shot pushes the lane, which is why rocket jump is better to take in laning phase.

I personally run flash teleport. A double gap closer or escape makes you annoying to deal with (though rocket jump is kind of clunky and unreliable at times) while teleport lets you free farm and join your team when a team fight starts or lets you take an unguarded turret very quickly.

All of these are viable picks. Some people prefer to have faster running speed after rocket jumping to ensure that the gap remains closed. Others prefer exhaust for its ability to completely shut down any AD champion. Others still prefer ignite to complement Tristana's early burst. Getting fed early can help snowball.

As for the other summoner spells, there are some pretty strong reasons not to take them (mana problems can be solved by smart usage, heal falls out, promote unnecessarily pushes lanes etc). However, remember that this isn't a ranked game (I really hope you're not trying out Tristana for the first few times in a ranked game...) and you can bring whatever works for you.

Early game - Farm up for your B. F. sword and other items. Getting out CS'd and losing your lane can already snowball for the enemy even if you've never died.

Mid game - Farm whenever possible but do not leave your team to team fight without you. Getting your items is important, but losing 4 kills to the enemy team and probably some turrets as well isn't worth the 30 CS you got by farming bot or top.

Late game - While your team is supposed to make an effort to protect you, this doesn't mean you can just mash your right click button and do stupid things. Yes, your team is going to try to protect you as best they can, but they can't really do anything if you get jumped by 5 people while split pushing or if you're in the center of a team fight auto attacking away. Take advantage of your 703 range and if lots of people suddenly start focusing you, QSS and rocket jump out. If you get downed and the enemy carry remains healthy your team's chances of winning the team fight are extremely low.

I play Tristana as a jungler. I build triforce and deal tons of damage. Here I dive Fiddlesticks at his turret, picking up the kill but dying in the process. It was worth it because I said so in the chat.

While this MIGHT be possible now due to the new jungles changes, Phreak's logic sadly doesn't work here. This is one time that you won't be dealing tons of damage with your triforce and jungling like a total boss.

Remember this is only a guide. Skillful use of a champion can only be learned through experience. If you fail one game, please do not be like the thousands of other solo queue carries that blame their jungler and never learn from their mistakes. If you could learn a champion perfectly in one game then you honestly shouldn't even be reading this in the first place.

Most importantly have fun! Play some Teemo Tennis with your friendly neighborhood Lee Sin or something.