Stains can be removed by polishing. If any rust appears, remove with a fine abrasive paper, or fine steel wool. With each use of your knife, wash clean and dry completely and lubricate. Most stainless steels don't need much care. Just wash and keep dry.
Natural woods benefit from an occasional rubbing with danish oil.
Wipe off excess. Clean with leather soap. Do not use any oils on the leather, as this will soften the molded shape of the sheath. If you will not be using your knife for a period of time, remove it from the sheath. Leather contains acid that could stain your blade or excellerate rusting.