I've never purposefully bred snails before, but I did keep a bunch as pets once, and they bred on their own. I kept them in a tiny terrarium. I put old fruit and foliage in there occasionally for them to eat. They would also eat fruity pebbles (I mean, it is the best cereal after all...) Keep the cage damp. Other than that, there isn't much to do to make them breed. You just gotta wait and see if babies show up. Mine had no issue breeding, and soon I had more than I could handle.