Getting a PERFECT means to rescue all villagers (3 per level). It does not matter if you get hit or die. As long as you rescued them all, it's a PERFECT. There are 36 levels in the game. First four worlds with 8 levels, and the final 5th world with 4 levels.
Here are videos for every level.World 1: Scarab Forest
World 2: Maddening Marsh
World 3: Galena Caverns
World 4: Lava Labyrinth
World 5: Queen DeRezzia's Castle
Note that following the above videos are guaranteed to get you the following achievements as well: