If your tub or shower is made of fiberglass, clean it by wiping on a paste of baking soda and dishwashing liquid with a sponge. Also, the same paste will attack hard-water and rust stains on ceramic tile. Use a nylon scrubber to clean it, then rinse.
Spraying the corners of your tub or your shower doors and walls with vinegar can loosen built-up soap scum. After spraying, allow it to dry. Then simply spray it down again and wipe clean.
Porcelain tubs and sinks can be among the trickiest for stain removal. Have you ever accidentally spilled an entire bottle of shampoo into your white tub and unwittingly let the mess sit there all day? That can certainly clean things up, but it's not really the recommended method. Instead, pour lemon juice over the stains, then sprinkle on alum powder (usually available in the spice aisle of the grocery store) and thoroughly work into the stain. If the stain doesn't come out immediately, let the mixture sit on the stain as long as overnight. The next morning, add more lemon juice, scrub again, and rinse.
Nonskid strips or appliques on your shower or tub floor can easily get stained and are often hard to remove. To clean, dampen the appliques and sprinkle baking soda directly onto them. Let this sit for 20 minutes and then scrub and rinse. You can remove the appliques completely by saturating each decal with vinegar to loosen the glue. (For even better results, warm the vinegar in a microwave or on the stove for about three minutes.) Let the vinegar sit for a few minutes, then peel off the decals. You should be able to remove any leftover glue with a damp sponge.
A bathtub ring requires a strong solvent. Try soaking paper towels or your reusable cleaning cloths with undiluted vinegar and placing them on the ring. Let the paper towels or cloths dry out. Afterward, spray the areas again with vinegar, then scrub with a sponge.