For a small scratch on wood, use a wood marker or wood fill stick to hide the scratch, fill it with wax, then refinish the area with lacquer. For deeper scratches that cut into the wood, sand first, and then apply lacquer. To repair a number of deep scratches, the finish may have to be stripped and the furniture re-lacquered. Small scratches on floors are repairable with colored lacquer pencils.
Tiny scratches in lacquered furniture can be filled with liquid wax and then buffed. Alternatively, apply lacquer thinner with an artist's brush. The thinner causes the lacquer to soften and fill the crack, which can then be waxed and buffed. The scratch can be hidden with marker and lacquer only if it is not cut too deeply into the wood. Otherwise, use sandpaper with 220-grit to smooth the scratch, spray on lacquer, sand again and then add a second coat of lacquer.
Stripping off the old lacquer finish is a major job that needs to be done outside with a respirator. Mix lacquer thinner and denatured alcohol in equal parts, and use a paintbrush to spread the mixture on a small section of lacquer. Use steel wool and a scraper to remove the lacquer. Go over the piece of furniture slowly, section by section. Afterwards, sand it over with fine sandpaper. Since the wood is clean, reapply any color of lacquer you choose.