Spray your stairs will an all-purpose cleaning spray, coating them with a thick layer. Wipe off the spray with a clean, soft cloth and allow the stairs to air dry.
Attach a piece of 120-grit sandpaper to an electric sander and run the sander across the surface area of the stairs. Repeat with a piece of 220-grit paper.
Wipe down the stairs when you're finished with a tack cloth to remove the dust from sanding. Tape off areas around the walls and railing that you don't want to get paint on with painter's tape.
Dip a 3-inch nylon brush in an oil-based primer and coat the stairs with an even coat, starting at the top of the stairs and working your way down. Allow the primer to dry for four hours.
Apply a light coat of oil-based paint to the stairs with your brush. Again, start at the top of the stairs and work your way down. Allow the paint to dry overnight and apply a second coat, giving it at least 12 hours to dry.
Run a measuring tape along the width of each stair and mark the center point.
Attach a stencil to the center of each riser with painter's tape. Your stencil can be anything you like. A number, a name, an animal silhouette; anything you like is possible.
Spray paint your stencils in place, holding the spray paint can 8 inches away and making uniform, short sprays. Remove the stencils and allow the paint to dry overnight. You've now covered your stairs in color, without the time and effort to paint the entire stairs.