A Good Player is one who doesn't wipe the party/alliance. A Good player will do mechanics, and even if their new, they can learn as they go (on the fly). A Good player will not tank groups of mobs in dps stance and use cooldowns effectively. A Good player will not only heal the party to ensure victory but will also contribute to damage output and make the runs go faster. A Good player will not prepull the boss before the tank goes to grab it. A Good player does what's best for the team (party) not just for him/herself.

Last, but certainly not least, a Good player is not a ***k. Treat others the way you want to be treated.