1. Remove the bumper from the car if possible. Use a ratchet and socket to remove all bolts and nuts from the bumper and use a Phillips screwdriver to remove screws from the sides of the bumper. Place the bumper on a stand or use a thin wire to hang the bumper by the bolt-holes on each side. Ensure the rafter used to hang the bumper is sturdy and won't fall during the preparation.
       
2. Sand the bumper using 120-grit sandpaper. Hold the sandpaper flat against the surface and sand evenly until the bumper is dull and no longer shiny.
       

3. Use plastic surface cleaner to scrub the plastic bumper. Use a microfiber towel to reduce the amount of lint that gets onto the surface. Rinse the area and allow it to dry completely.
       

4.  Wipe prep solvent over the plastic bumper using a clean microfiber cloth. Wipe the solvent in one direction so dirt particles aren't wiped back onto the clean surface. The solvent does not need to be rinsed or cleaned off.
     

5.  Sand the plastic bumper with 400-grit sandpaper and water, keeping the sandpaper soaking wet while sanding. Sand evenly so that the bumper is very smooth and dull. Rinse the bumper and allow it to dry completely. Wipe the plastic bumper once more with a tack rag to pick up any remaining dust or dirt particles. It is now ready for paint.