[quote=Titanic]
You should probably classify what types of magic are allowed (Healing, elemental, etc) and whats the limit.
[/quote]

Alright, how about an element system?
Fire is countered by water, which in turn is stopped by earth, which is vulnerable to fire.

Or perhaps a more school-based system, where mages must train in a respective field first, and can't work other types of magic until they've had training.

Or, we could have a Warp-based system, like in Warhammer 40k. Mages need to put themselves through intense psychological training before they can perform even basic spells, as they must reach into a dark, vicious world, where monsters claw at ones mind in an attempt to send them crazy.

Or, a dust-based system. Magic in its purest form is a substance, which is harvested, refined and used for combat, but said substance is somewhat rare, so you don't have a lot of power with it.