the easiest is to take off the seat. then you basically start out with a coarse grit paper. and try to get it smooth. you can use a filler for any bad gouges or scratches. start with like a 180 grit. then work your way up to a 1000-2000 grit paper. at that point you can use some mothers polish compound and a couple bads from an auto store. only to finish with a nice wax coat. basically you remove a layer of material to get a glass smooth surface. then put on a nice clear coat.