Wipe away any dirt or dust from the plywood before you begin sanding.
Use 180-grit sandpaper to sand the plywood. Stroke the sandpaper over the plywood in the direction of the grain 3 to 4 times. Further sanding can create too many grooves in the surface and cause the layers to peel up from the ends of the plywood. This grit addresses any imperfections in the wood.
Sand the plywood with 200-grit sandpaper. Follow the grain for 3 to 4 strokes along the surface. This finer grit smoothes away the lines the 180-grit paper creates when grinding away the imperfections.
Rub the plywood with 220-grit sandpaper making two passes over the surface. This grit gives the plywood an extra smooth finish as the final sanding before applying stain or finish.
Wipe the plywood clean of sandpaper dust with a clean cloth.