To get effortless experience follow these simple steps:

• play through the game like normal until you get your bat familar.
• at this point go back to near the start of the game where the zombies keep coming out of the ground.
• then all you do is stand on the step on the stairs where the zombies can't reach you and turn your bat familiar on. Just make sure that you are far enough away that the zombies won't hurt you if your familar misses one of them.
• The bat familar will kill most of the zombies that appear, also make sure you are looking in the direction of the zombies or the bat will not hit them.

The best part about this trick is that the familar will kill the zombies and both he and you will get the experience making this absolutely simple in gaining levels. In three hours my bat went from level 2 to level 60!