Aside from learning your class, the next most important thing is learning the game that you're playing. You will need to learn the gameplay, games mechanics and about the game. It's important to know what your role is in a group when you play the game. Along with what your group members roles are, when you know this it will make it much easier to fill in their weaknesses with your strengths and vice versa. Also when learning the game, learn where things are in the game. Learn each area, dungeon, City, Town, Raid Instance etc etc. When you see someone pull one mob out of a pack of 3 in a dungeon, ask how he did it. Get some advice learn the secrets of how to Dodge mobs and show your next group how you did it.

You'll notice when you learn more about the game, the classes and such you will slowly start to become better. Another crucial thing to learn about, aside from game play is the game mechanics. Mechanics will take a lot more coordination to learn and get used to. The most important game mechanic that I think to learn is Terrain and Jumping. Learning how high you jump and the distance you jump in almost any game is important. Expecially a PvP game, being able to jump over a fence when a pissed off Warrior behind you could save your life if he doesn't make the same jump. Learning your Jumping distance helps as well. Once you learn your jumping distance you will be able to take shorcuts. Like jumping off a bridge towards the end and landing ahead of anyone who ran over the bridge and then turned.