Paint adheres better to a surface that has been abraded. Nylon pads provide adequate abrasion for paint adhesion, as does sandpaper. If the surface is smooth to begin with, all you need to do is scrub with the nylon pads. Use sandpaper to level a rough or peeling surface, or if there are many coats of paint on the surface. Sanding lessens the thickness of the old finish, which reduces the possibility of peeling later. Sand by hand using a sanding block, or use a power orbital sander. Begin sanding with 80 or 100 grit paper, depending upon how much material you need to remove to level the surface.