Shower
In order to clean the shower, disinfect the shower head and make it shiny again, you need some apple cider vinegar, a rubber band, and an empty plastic bag.
Pour the vinegar into the plastic bag, secure it with the rubber band to the shower head, in order it to be submerged in the vinegar completely. Leave it for an hour and rinse with water.
Sink
Mix some lemon juice and potassium bitartrate, and apply their mixture on the sink. Use a toothbrush to clean it, and rinse with water. This will effectively remove the rust.
Floor and tiles
Mix a teaspoon of your usual dish washing detergent, 1/2 cup baking soda, and 1/4 cup hydrogen peroxide to clean the tiles and floor easily and quickly.