If you die too quickly, the basic answer is to put points into Vitality. Else, try too see which type of ennemies deal the most damage (ranged, magic, melee), and try to boost that type of defense.
As a mage, you can "forget" Strength, as it boosts melee defense, and you should kill most mobs before they get close. Vitality is still needed as a Mage, even if it's not your primary stat.
You don't have to put tons of points into Spirit, as with high Intelligence, your mana replenishes faster, combined with the skill that reduces mana use (I'd say as much in Vitality than in Spirit at first, later on you may forget Spirit entirely).
I had the same problem (health) on my first run, have you thought of putting points into Ghost ? The ghost has a healing skill, which is very usefull, but you need to put more than one point in that skill.
