Clean your bathtub with a bathtub cleanser and a sponge. Use a clean rag and the cleaning solution provided in your bathtub refinishing kit to wash away any leftover soap scum or residue from the bathtub cleanser. Let the tub dry before proceeding.
Use the sandpaper to sand the entire bathtub. Rinse off the sandpaper with water. Use another application of the cleaning solution kit, this time using the cleaning pad that came in the kit. Rinse off the bathtub with water and dry it out completely with an old towel.
Apply primer to the bathtub using paper towels. Let it dry.
Apply putty with a putty knife to any cracks or pitted areas on the tub. Sand it with the sandpaper when it dries. Rinse off the sandpaper grit with water and dry out the tub with a towel.
Tape off the bathtub fixtures with tape and a protective paper. Pour the base paint in the kit into a paint sprayer. Spray the bathtub with the base paint. Let it dry completely; this should only take about 30 minutes.
Pour the topcoat of paint into the paint sprayer and spray over the base paint. Spray evenly so you don't leave any streaks. Don't plan on using your bathtub for at least three days so it can thoroughly dry.