Caitlyn is a very heavy AD carry and if used properly can carry a team. Caitlyn's high range can allow her to auto attack enemies from a very far distance, this is why she is also a great mid.

The dorans blade is always good for any DPS carry, and the beserkers greaves are good for attack speed aswell. But the two B.F swords are very useful because early game no one expcept tanks has a high defense so you piltover peacemakes does a ton of damage and your auto attack is good too. Also the early game damage of your ulti will get you fed easily.

The runes for Caitlyn can very a lot. I tend to go for armor pen. just because its good for AD carrys. The extra crit damage with the seals comes in alot end game and the attack speed glyphs help out early game.

I got 21 and 9 with Caitlyn because she is heavly AD based but also needs some utilities such as CD reduction, its very useful and the +gold helps alot too.

Rush your Piltover Peacemaker, this is because this skill does a ton of AD damage and can really hurt someone early game, with your traps try to place them across the lane so the enemy has trouble either leaving their turret or running back to their turret, soon enough one will get annoyed enough to go and step in your traps and thats when you just own them.

I normally do Exhaust and Ignite because those two spells are great together and can never normally send you the wrong way.

Caitlyns heavy net is amazing at escaping, it can be used to go through walls and also if it hits an enemy it slows them, this move is great for escaping a bad situation, but be careful it has a very high cooldown.