I've never done it, so here's advice from someone who doesn't know first hand... they say that they like coffee grounds and corn meal sprinkled on top of the ground. You're supposed to keep the soil slightly moist but never wet as they drown.
I do know first hand that worms create rich, loose soil that will grow anything! If you ever want to plant a garden, find an area that has a lot of worms and the ground will be just right for it.