For a mage, Karifean's set is invaluable. The Foe: 100% = Steal gambit is very useful for your lead character. You'll generally want to include a Foe: Flying = [x] in there when you start encountering flying enemies with greater regularity. The x can be anything from magic or a thrown item, but you get telekinesis really late in the game unless they've changed that and of course, with the job system not everyone might have offensive magick.

But the general pattern of healing, support, attack works well. You'll want your revival options first, followed by one or two healing gambits, possibly arranged like so:

Ally: KO = Phoenix Down/Raise
Ally: <30% HP = Cura
Ally: <50% HP = Cure

Or something like that. A general healing gambit, but supplanted by an 'oh smurf I need healing NOW' gambit with lower HP. Remember though cure now has an AoE, which is useful.

Essential support buffs like Haste, Bubble and Protect come next so they can be cast mid-battle, followed by an attack gambit or two. The attack gambits will obviously vary. For a mage, the 'elemental weakness' set is great, while physical fighters can probably get away with a more basic attack command, though feel free to experiment with all the different ones. I sometimes like to activate one that targets the enemies with the lowest HP, which is great in mob fights.

Of course the great thing is you're given all the gambits when you unlock the system. I had to wait forever to get the elemental weaknesses.