It doesn't necessarily work like that, but it's a way to start stabilizing a strain you like very much.
The offspring of the S1 (first selfed) generation are not necessarily going to be uniform in their traits, but you can grow out that population and choose the female that most closely resembles the mother, and back-cross her (also using pollen from the initial hermaphrodite flower on the desirable mom).
The other way you can do this is find a strain that closely resembles what you like, and use a male from that strain to give you the Y chromosome that will make repeated backcrosses to the original female a lot easier.