Mages in World of Warcraft are not the most gear dependent class in the game, but while leveling you should certainly take steps to ensure your gear stays up to par.  One of the most important stats for mage leveling is spell power.  Spell power affects how much damage your spells do, and as such, it affects how quickly you can kill your targets.  Whenever possible, you should be going for gear equal to your level with spell power as the primary stat.  If you do this, your killing speed will increase, and your leveling will go by super fast.