How should I apply water-based polyurethane over an oil-based stain for the best results?

To apply water-based polyurethane over an oil-based stain for the best results, make sure the stain is completely dry before applying the polyurethane. Lightly sand the stained surface to ensure adhesion, then apply a thin, even coat of water-based polyurethane using a high-quality brush or roller. Allow the first coat to dry completely before applying additional coats as needed.