No tricks to this. It's a hack'n slash game so just get to hackin'n slashin. The most common enemy early on are little goblins. You should dispatch 30 by the end of level two. If not, they seem to spawn infinitely during the boss fight at the end of the second level. Just avoid the boss and keep killing goblins. Or play normally and it will happen naturally very soon. This took me about seven minutes.