All 'active' pet skill stats are driven by thier stats. When you mouse over any of the stats, it will tell you what that stat affects.
Boosing the stat will boost the skill. Once the skill is maxed, your only hopes are to
a: get a 'passive' trait like Eager that will boost that stat b: breed the pet with something with bigger stats, like your class pet or one of the higher drops.
Warning: the last is both potentially expensive and time consuming. I've found it is best to relegate a grand to the status of 'pet trainer' because they can earn money the fastest, and have access to the best dropped snacks.
As your pet gains experience, the stats for some of it's talents (be it accuracy, resistance or damage to name a few) can increase.
My pixie queen pet named luna has a 2% life accuracy talent that can increase as I level her up, while my other pixie queen named king dexter gives the same percentage in life damage (again, which can increase as he levels up).