Leveling is really simple in H/M. All you have to do is to travel to high level areas (around 40-50) then find a tower with slime spawners inside. Then build up a tower of dirt in the corner of a floor so you can stand on it. For a warrior, just step up once the creatures have amassed to kill them. For a mage or ranger, just snipe them from above. You should power-level pretty quickly.