The good and bad thing about pet battles is that it's fairly open ended. I do think getting your Safari Hat is a good goal to set though. Read up on the boss giving you trouble (Okrut? Payne?) and then level the pet(s) you need in order to pass him. It gets tougher from Northrend on up, but don't get discouraged! Tamer battles are more like a puzzle than anything.
xoxo, Your Pet Battling BFF, Tamer Liopleurodon.