Fill any holes with wood filler (overfill) and let dry. Start sanding with coarse sandpaper and work your way to fine. Vacuum with a soft bristled brush. For paint grade, prime and apply multiple coats of paint. I always paint the insides first, then the outsides and finally the trim. For stain grade, you may wish to apply a wood conditioner first, then stain, and finally finish with a varnish or polyurethane sealant.