When I play a Light Armor character I often put a lot of points into Health.
Magic resist is the best defense. Enchanted gear helps but it's recommended to get some permanent buffs as well, for example Agent Of Mara gives permanent +15% magic resist.
The Atronach Stone is always a good option. +50 magicka and 50% chance to absorb spells at the cost of cutting your magicka regen in half. Worth it for most warrior and stealth characters, and even some mages.