You can deviate according to your preference (i.e. melee-armored mage, crit type mage, etc) but the best MG around would be pure int. Why? In addition to dealing high amounts of damage, we come personally equipped with a skill that enhances our defense, can teleport instantly (though the skill has a cooldown, its relatively fast compared to a warrior's), and since magic never misses, you'll sure to land all of those attacks in.
Both defense and critical can be compensated with items. For defense, fill your armor slots with def stones (lvl 12 recommended) and you can easily reach 20k+ def even without buffs. For critical, wear accessories with critical %, especially rings. If your a sucker for fast casting then dont worry, the mage's sutra skill more than makes up for this.
This is all for the mage guide. I made it short since we're playing in a private server and details are too often neglected. Have a nice day :D