Dragonica problems. Help?

I have a level 8 thief and I die over and over again when doing the missions. I've heard complaints that combat is too easy, so I must be doing something wrong. I'm currently making air combo launch, aerial frenzy, double attack, and cutdown. My strategy is either to attack outright or use air combo launch and then follow up with aerial frenzy. But, it's weird because aerial frenzy rarely hits the monsters more than once. It just hits them once and they they fall to the ground. Rarely ever do I get a large combo with it. And bosses absolutely slaughter me. I really want to play this game, but if I'm failing everytime at these missions I don't want to. Help?!