I wipe mine down with towel after every shower. I've never had to heavily clean the side walls and ceiling, spot clean a little.
The floor I use either 409 (spray, let soak, wipe up) or for a real nice look I'll go over it with automotive cleaner wax. The finish on my shower is glossy fiberglass.
But I do think the key is to wipe it down after each shower (or two consecutive showers)