I use the cheap hair shampoo. It removes all the soap scum and leaves it shining. It also helps if after taking a shower the walls are wiped down. (My husband always forgets)If not, the shampoo still works great. We have hard water from Lake Erie. Good Luck.

The magic sponge is awesome. My husband is an auto mechanic and has his own shower, needless to say, I don't get in there as much as I'd like and the magic sponge works wonders with any non-scratching cleaner. I don't even have to scrub.

you can also coat it with RainX (used on car windshields) the water will just roll off.
We have a tile shower with glass doors in our MBR and we wipe it down after every shower with a towel. I haven't had to clean the tile yet......