The point of this post is not how to clean the mildew and soap scum, but how to reduce or prevent it from accumulating in the first place. You’ll need to start with a clean surface. After you scrub down your tub/shower, then try this!
Early in our marriage I remember seeing my husband use furniture polish on the tile in the shower. I thought it was really odd, but he explained that it was a little Marine Corp trick to keep their showers shining bright for their inspections. Once you scrubbed down the tiles, you spray some furniture polish into a rag (OVER YOUR BATHROOM SINK) and wipe down the walls. Then buff with a soft, dry towel. This leaves a sleek and shiny finish. Soap scum will not accumulate as before and the water would bead right off. It also creates a barrier to help prevent mildew from forming.