From Aaron and clay, I have personally learned that it's okay to not have a plan all the time. It's okay to change your mind on the fly. It's even okay if you punch a hole in your wet clay mug, because you can patch it up in seconds, and you might just create something more beautiful as a result.
Aaron truly understands this craft and can easily recite the appropriate techniques and jargon, but you'll learn very quickly during a session that there are very few rules and absolutely no expectations. Just show up.