Fill a bucket with 1/2 gallon hot water and add 1 quart white vinegar. Dip a cotton cloth in the diluted vinegar solution and wash the single stage urethane paint surface to remove all dirt and debris.
Rinse the surface with water. Hand-dry with cotton cloths.
Tackle any bumps or flaws that detract from the look and shine of the paint surface by wet-sanding them. Wet a piece of 2000-grit sandpaper with water and sand the areas until they're smooth and blend in with the surrounding paint. Rinse the sanded area with a damp cloth and dry it with another cloth.
Squirt a quarter-sized amount of polishing compound onto a foam pad. Rub the polishing compound onto the surface of the single stage urethane, moving the pad in a back-and-forth motion. Repeat this step until the entire surface has been polished.
Rub the polishing compound off the single stage urethane with a buffer and soft buffing pad. As you buff the paint surface to remove the polishing compound, the shine will be restored.