Suzanne wrote that she appreciated being able to do rolls from a kneeling position first, and I think that's a good and a safe way to start. I also feel that nage's role (no pun) is very important. Nage should set uke up for success, especially newer ukes. Nage should never throw uke harder or faster than uke can handle, at least not by much. Uke, on the other hand should never attack harder than he/she can fall. Becoming proficient in ukemi helps your technique immensely. Ukemi is not just falling; it is falling in such a way that you can get back up.