Betsy, I don't know how many bulbs you got but I would say to put them in the ground if at all possible. They do better in ground and you don't have to do too much once they're in. That said, many people do pot lilies as well. I think the key is not to keep them too wet or they will rot. As far as mix goes, a good potting soil with some sand mixed in should be fine to allow good drainage. Pot size would be determined by how many bulbs you are putting in a pot. Don't go too small as they will dry out quickly and not allow the roots to spread out.
