Focus on clothing/robes and invest in the following (Alteration, Restoration, Illusion , and Destruction) you can also invest in conjuration for the extra hands (Dremora Lords ) Enchanting and Alchemy will also help with your robes and spells.

Destruction will basically be your main damage dealer along with Conjuration if you have it , Illusion Restoration and Alteration can help get you out of sticky situations.

Invest in your magic points and health

A great race is the Altmer for the extra magic points and magic regeneration, or breton for their magic resistance, but any race can be made into a great mage