I recently did a "generalist" magic system, for a campaign I am working on - this is how I broke it down:
Affliction, Divination, Healing, Infusion, Movement, Transform were all one skill- these all involved adding or removing abilities, senses, health etc.
Abjuration, Creation, Hexes, Illusions, Summon are all one skill - they involved creation of some sort (effects, items, illusions, creatures).
Compulsion, Enchantment are one skill - they involve mind affects / mind control.
Displacement, Evocation - energy or space manipulation.
Haven't played it yet to see if the balance is correct; was looking for thematic connections more than balance ones.