The three skill trees of rogues are assassination, combat and subtlety and are only meant for improving damage since the rogue has no support talents, he can't tank or heal. The three skill trees require different types of playstyles. Sublety is the recommend PvP tree, but of course you don't have to spec in it for PvP. The rogue ideally has the initiation strike out of his stealth and can sometimes rule the fight. Skills like Kidney Shot and Cheap Shot help to stun the enemy so they can't dodge the rogue's attacks.

The assassination rogue is very often specialized in daggers since his talents focus on daggers. But attacks from dagger rogues only do the most dmg when attacking from behind and out of stealth. Furthermore the armor rating of the enemies shouldn't be that high.

It's quite the opposite as a combat rogue. Combat rogues are best suited for instances because they deal more damage with swords, fist weapons and maces and don't have to attack from behind or out of stealth. It's worth it to gain high haste ratings for maxing out damage.

The subtlety tree is made for PvP. Many talents in this tree are quite essential for playing PvP. The talents focus on hiding the rogue and survival. For example, you can make your rogue 15% faster when stealthed and you can improve his stealth so other classes can't see early enough to avoid a stun.