How do you guys raise skills that have fallen behind?

[Arcon]

The cured amount makes very little (if any) difference. I didn't notice it at all, personally, but I can't rule it out. It just seems extremely unlikely based on my experience with it and based on the skillup mechanics for every other skill, none of which depend on the potency of the spell or attack. Curing undeads on the other hand will give you extremely high skill, due to being offensive. All offensively cast spells get a skillup bonus (or more accurately, all spells cast on NPCs, Besieged NPCs work as well).

[Mirage]

As long as the besieged NPCs are high enough level.