Sanding plastic, especially plastic car body parts, is essential if you need to get a perfectly smooth finish. The primary thing to remember when wet sanding plastic is to use a light touch. Let the paper do the work. Never sand in just one direction as this will result in scratches that are difficult to cover later. Instead, sand in a circular motion, using circles of differing sizes so there is no discernible pattern to your sanding. Use a circular foam sanding pad that accepts adhesive-backed sandpaper. A nice foam pad allows you to sand both flat surfaces–as well as surfaces with a curve to them. Start with a 200-grit paper and progress to an 800-grit paper for a perfectly smooth finish every time.