Caitlyn is a ranged champion, its a good champion to get some kills but also is a helper of the team and her strongest point is kill never let a low hp enemy live.

PROS:
Have an awesome ranged demage
Can kill people at giant distance
6 in 6 hits grants you a critical strike
Can cross some walls
CONS:
Squishy
Can only cross small walls
You are one of the first being focused

I recomend you to get some Mark of Desolation it will help you a lot at early game.
Seal of replenishment this runes are the most important to solo lane if you have this runes you will never go out of mana.(You will go out of mana if you starting spamimg skills)
Glyph of focus this are the less important runes but they still are important, with this you get 5.85% cooldown reduction its pretty good because you most keep you ulti up for any emergency situation.
Quintessence of Desolation as I say at the first runes i say the samething about this ones, because they are both Armor Pen.

Ok i think you should take 21/0/9.
Lethality this is the most important mastery at ofense build it will improve a lot your passive its pretty hand at early game.
At the utility build the most important masteries are perseverence and meditation because the Mana regen runes arent enough to full your mana bar.

If you go 3vs3 start start with the doran´s blade if you go 5v5 start with vampiric scepter.Why? Doran´s blade will make you more tough, pretty nice to first blood.And the vampiric scepter do a great combination with the mana regen runes because will never have to go base because you have a good regen and lifesteal.
Ok about the Phantom Dancer and the Madred´s bloodrazor ir you are vs a tank on your lane take the madred first and the Phantom Dancer, if you dont are vs a tank buy the Phantom Dancer and than the Madred.
Ok about the Frozen Malet I should buy one late game because Caitlyn becomes a little squishy late game and the Frozen Malet aplies slow efect pretty good for chase.

Piltover Peacemaker this skill is perfect, with this you can demage the enemy minions and the enemy champions and at the same time be at a safe distance.
Yordle Snap Trap you can use this on the weeds and when you are being followed by an enemy champion put a trap on his way so they will be snared and detectable.
90 Caliber Net use this to slow your enemy but whatch out you will be knock back but calm down thats a good thing you can use this to cross walls and to run safely from an enemy.
Ace In The Hole this has a gigantic range and its awesome to solo lane when your enemy is with low hp you cant use this to take him down.But watch out any enemy champion is on the bullet way they can block the bullet and some his mate.

You should learn all skills because you need him all at least at rank 1 but you main skill is the Piltover PeaceMaker when you use this try to hit all the enemy minions incoming to weak him all.Ok now why should you learn the other skill at least rank 1? Because with the Yordle Snap Trap you can trap the bushes and reveal some enemy trying to gank you.And the 90 Caliber Net is pretty good because at rank 1 aplies a 50% slow and knocks you back, for other words keeps you away from a slowed target.

To help your mates you can do this:
Place traps on the bushes, if any enemy fall on the trap all the team will see that any for some seconds.And you can also place a trap to where the enemy is walking to snare him on the fight.
You can also help a friend reaching the enemy slowing the enemy with the net or you can slow your enemy to allowed your mates to run.

Flash, why not ghost? Because Flash made a good combination with 90 Caliber Net knock back.
Flash and Exhaust to 3vs3 and Flash and Teleport to 5vs5.

Basicly caitlyn is a crit champion as any crit is a little dependent of atack speed but auto atack isnt all your skills remenber that.
NEVER use your ulti to steal use only if the target is geting away.
Cleaning a lane with caitlyn is very easy, especialy if you hot all the minions with the Piltover peacemaker.
To do a good demage with catlyn you just have to choose correctly the order of the items becuase you dont have to follow the order of my items so hard as say.Check your oponents and decide what should you buy first.
And thats the summary now have fun playing and dont forget to vote.

5lyk