When finishing and preserving a wooden bookmark, it is important to choose a protective finish that will withstand wear and tear. Some popular options include polyurethane, varnish, or wax. Apply the finish using a clean cloth or brush, and make sure to cover the entire surface of the bookmark. Allow the finish to dry completely before handling the bookmark. To keep your bookmark looking like new, avoid exposing it to moisture or extreme temperatures, and store it in a dry, cool place when not in use.