Watch what other mages are doing. Learn from their mistakes, learn from their good plays.
Mages were a mystery to me too. After making friends with good ones and duelling them over and over (I main a DK) + experimenting on my own, I've managed to learn the class somewhat.
You can make a mage on Blackrock and look through the talents and spells thoroughly, get some idea what you can do with them.
-
EDIT:
/agree with above. "That is what makes mages hard, not the skillcap but the skillfloor."