For PvE, it is best if mages work to optimize their AoE moves. They can hit about 4 or 5 enemies at a time, and putting out that much damage that fast leads to faster levelling.
They should max out Meteor, which pops up enemies in an area of effect, and maximize Air Combo, which also has an area of effect and hits midair enemies for sizable amounts of damage.
The Passive skills and buffs that raise magic attack will amp up the damage of the Meteor and Air Combo, making levelling even faster.
The healing skills can turn your mp into hp, which can be useful. They won't speed up training, though they are a good thing to get second.
All the offensive active skills besides Meteor Shower and Air Combo are weaker than Meteor Shower and Air combo. They can be ignored.