Well, I am still figuring this game out, but I feel that Mages need a deep magicka pool. Regen is just as important, so I go for the Arch-Mages robes as fast as I can, along with getting the dragon priest mask that gives the 100% regen. Then, I cast Calm, Fury, ___Flesh, Bound Bow, Muffle, or whatever else I think I might need before that particular battle. Illusion & Conjuration are awesome, but I would also have the real thing for back up, just in case.
I haven't tried the higher difficulties yet, but that is in my future......maybe my next Mage build....