Fill a 16 oz spray bottle with a mixture of 1/4 cup of Blue Dawn, 1 cup of vinegar and if you want a fresh smell a few drops of orange or some other essential oil. Then fill the rest with water. Swirl around and spray the shower. Walk away. In half an hour or so take a big sponge, like a car sponge, wet it, wipe it down and rinse. I usually take my shoes off and get in. Takes a few minutes if you do this once a week.

Two additional tips - use liquid soap when you bathe. There will be much much less soap scum to deal with than with bar soap. And buy a shower curtain like the hotels use with the snap in nylon liner. When you wash your towels snap off the liner and wash it. It will always smell fresh and no mildew will accumulate.