Introduction:
Hello, I'm CrazedSeal. This is my first build on Mobafire, I visit regularly to check out builds for champions I just bought. This is a Caitlyn build, but the items may work on other champions such as Xin Zhao and Tryndamere.

Pros:
-Lots of Damage. 1.2K Headshot Critical
-Lane Sustainability
-Fast Attack
-Damage goes well with Abilities.
Cons:
-No Defence
-Slow Movement at Start
-Can be easily shut down
-Needs to be fed early.

Runes:

-Marks of Desolation - Getting some early Armor Penetration will help do more damage against targets.
-Glyph of Furor - When you critical Strike you will do more damage.

-Seal of Alacrity - Gives a bit of attack speed, useful for last hitting minions.

Items:

Phantom Dancers - Great Items, gives a lot of attack speed, critical strike, and Movement. A simple fact is that two of these gives the amount of Movement 2 Boots. The Attack speed allows Caitlyn to dish out the damage quickly, combined with the critical strike you can end up killing people in 3-4 Shots.
Vampiric Scepter - Good Early game, allows you to be in lane for almost ever unless your under heavy harassment. Shooting minions and enemy champions will allow you to get the most out of this item.
Bloodthirster - Great Item, especially good for caitlyn, it gives 60 Damage (+40 When Maxed) and 15% (+10% when maxed) lifesteal. Getting about two will increase your damage a lot, and giving 50% lifesteal. Doing a 1.2K Headshot will give you a nice 600 Life back.
Infinite Edge - Another great item for caitlyn, gives a massive 80 Damage, 25% critical Strike and makes your critical strikes do 250% instead of 200%. This is a must get item for any carry.
Berserkers Greaves - Good early game item, 25% attack speed and 2 Movement. You replace these with a phantom dancer as you get much more.
Black Cleaver - An extra amount of damage, the special thing about a black cleaver is its armor penetration. Every shot reduces your enemies armor by 15, this stacks 3 times, in total makes your enemy lose 45 Armor, combine this with the runes, that is an amount of 60 Armor gone.

Which Lane?

Good thing about caitlyn is that you can take either of the three lanes. Though the middle lane is preferred. As you get more experience, gold, and only one target to shoot.

Harassing Your Opponent:

With Caitlyn its quite simple. Simply piltover the minions, and the champion if you can, If he gets close Auto attack him alittle. If you get a headshot, and if the enemy is close you hit him with it. When you reach level 6, this is when the fun begins. Caitlyn has slight mana issues if you spam her abilities too much.
Try and auto attack the enemy to a low health point (Below 150). Then use your Ace-in-the-Hole to finish him. ONLY IF HE ATTEMPTS TO RECALL OR HIDE BEHIND THE TOWER. Doing this while hes in your face may get you killed.

Piltover Peacemaker - Use to harass your opponent, and/or clear minion waves. This ability pieces through all units in a straight line. Use this to farm and harass your opponent.

Yordle Snaptrap - Good tool for stopping enemies reaching you, and can prevent deadly ganks by placing in the bushes.

50 Caliber Net - Excellent slowing tool. Use this to slow down a charging champion, it does a bit of magic damage. Can make you go through some walls.

Ace in the hole - Great finisher move if the target is out of range. Has great ad scaling. Though blockable by enemy champions.

Well. I can't think of anything more. If you manage to complete the guide ingame. Go around and attack people. Get Red, beat dragon, defeat Nashor!( Not by yourself )

This build can be countered in many ways, such as thornmail, armor items... ect...

-CrazedSeal