I was giving my July Good Housekeeping magazine a final once over just today and Heloise answered the exact same question. She said that after you take a shower, when the glass is still steamy, "pour a bit of cheap hair shampoo or liquid dish soap (both break down grease and oils) onto a plastic scrubby or sponge that won't scratch the glass. Apply and let sit for 5 to 10 minutes. Rinse well, and repeat this process if needed or until the buildup is gone." After that, keep a squeegee in the shower and wipe the glass after each shower.