I suggest minimize your mana costs and don't overkill on targets that don't need all that burst damage. The more you have to sit and drink, the longer it's gonna take to level. I personnally suggest leveling with all frost and putting your frostbolt on round robin. Other than that, you wanna level with all 5, and quest. I couldn't do many instances at low levels with the 5mages, but i had them all RAF so questing was worth it for me.