This is my first Guide.

Caitlyn is one of the best AD-Carries. Her enormous range and her passive are perfect for poking the enemies on your lane and get controll over them. When laning Caitlyn you'll also benefit from her abilities, which are quite good to zone other players.

As runes I recommend flat armor penetration Marks, 3 armor Seals, 6 attack speed Seals, flat damage Quintessences and flat damage Glyphs.

Explanation:

- Flat armor penetration Marks: Gives you more damage against your enemies on your lane, for example Taric or in generall against every other player

- Armor Seals: The armor seals are for making you more durable on your lane, meaning you get less damage from your enemies.

- Attack speed Seals: These runes are important because they let your Champion last-hit faster and, if it comes down to a fight with your enemies on your lane, you will do more damage to them.

- Attack damage Glyphs: More damage. Therefore easier last hitting and more damage to your enemies.

- Attack damage Quintessences: Same as Attack damage Glyphs.


Masteries:

I guess the offense masteries are pretty clear. More damage, attack speed, etc. The part that needs explanation is the defense and utility part. At utility I've reduced the CD of the Flash summoner spell. This is because Caitlyn is quite slow until you get Phantomdancer/Seal. Bot lane often gets ganked and the CD reduction on flash is quite important to escape those ganks.

I have added more armor in the defense mastery to make you more durable against enemies on your lane. Also there are some points on Tough skin. These are here so you take reduced damage from enemy minions while fighting against your enemies. The more live per level mastery is skilled to give you more live - so you can stay on your lane longer.

I pick Yordle snap trap first because you can zone enemies or prevent enemy supporters from entering your brush.

Piltover Peacemaker is a very important damage source against enemies because of it's range. Make sure to max it first.

90 Caliber net is important to get away from ganks or enemies when you are low life or getting chased by them. Skill it by level 3 and max it last.

As summoner spells i recommend Flash and Ignite. Ignite is a powerfull weapon against enemies with a high amount of life leech. Flash helps you getting away easier. You can also use ghost, but i dont think that it is that effective.

Pros:

- Caitlyn is a high ranged AD Champion, which allows you to poke your enemies without getting damage yourself
- Good zoning ability
- high damage output and aoe abilities
- Able to hold enemies in place with Yordle Snap trap

Cons:

- Quite slow and therefore easy ganking target

When playing Caitlyn on Bot-lane it depends how you start. If you have supporters like Sona, Soraka, Taric or Alistar with you, you can start with dorans blade if you want. Caitlyn is quite a slow champion so I recommend boots and 3 Heal potions first. If everything goes well on your lane buy a B.F. Sword. If you have troubles on your lane buy dorans blade. After B.F. Sword i recommend Vampiric Szepter for more lane sustain. The BF Sword is used for Infinity Edge. If you have completed building your infinity Edge, focus on building Phantomdancer. Phantomdancer is a great item because it gives you a higher crit chance (the crits are 250% instead of 200% thanks to Infinity edge) and more attack speed so you can kill minions and enemies faster. Next you buy a Bloodthirster and Last whisper. These items give you more damage and armor penetration. Quite important against Champions with much armor. As a last item i recommend Guardian angel because you will be focused by enemies during team fights. This item helps you doing more damage to your enemies + they might not focus you anymore ;) .

As Supporters I recommend Soraka or Taric.

Taric and his stun are powerfull against enemies because if he stunns an enemy focus him and place a Trap behind him. Therefore you can do more damage on enemies and force them to base quite fast.

Soraka on your lane is great, because of her heals and her ability to give you mana.

In team fights you'll get focused. See that you are behind your team when the enemies engage, giving you time to do much damage. If you are getting focused use the trap to hold back your enemies before they can do damage and slow them with your 90 caliber net, giving you distance between them and you as well.