I’m of the theory that showers are too difficult to clean from the outside, and I much prefer to clean mine while using it.
I keep a scrub brush and spray bottle of hydrogen peroxide in the shower for a quick all-over scrub of the walls, floor and crevices around the door. Periodically the floor needs a scouring, which requires baking soda and a little more elbow grease. A daily spray of hydrogen peroxide in areas prone to mold help keep it in check, as does an all-over squee-gee to remove water drops before you exit the shower.
Tubs that are used often will also need periodic scourings with baking soda and water. On a weekly basis, spray with vinegar water and wipe down with a damp rag, then rinse.