Mirrors: The easiest way to clean a bathroom mirror is to leave the bathroom light off, the light's make the mirror hot and harder to clean. Use glass cleaner and a microfiber cloth, if you don't have any microfiber cloths use paper towel, this will prevent streaking.
Glass Shower Doors: The best way to keep your glass shower doors looking good and spot free, is to keep a squeegee in your shower, squeegee your doors after every shower. To prevent soap scum build up first, wash down your shower doors and dry them. Next wipe them down with some lemon oil, baby oil, or even furniture polish buffed on the door can work. This will make your doors easier to clean and have to be cleaned less often.
Shower Curtain: Prevent soap film build up on the bottom of your plastic shower curtains, by rubbing baby oil on the area. If you already have soap film build up you can place several large bath towels in the washing machine along with the shower curtain. Add 1/2 cup vinegar. (if moldy us 3/4 cup bleach instead) Remove the curtain before the spin cycle starts and hang it up immediately.
Unwanted Decals: To remove unwanted bath decals, heat the decals with a hairdryer and pry off with a plastic spatula.