How can I effectively apply polyurethane over an oil stain to achieve a durable and long-lasting finish?

To effectively apply polyurethane over an oil stain for a durable finish, follow these steps:

1. Ensure the oil stain is completely dry before applying polyurethane.
2. Sand the stained surface lightly to create a smooth base for the polyurethane.
3. Apply a thin, even coat of polyurethane using a high-quality brush or applicator.
4. Allow the first coat to dry completely before applying additional coats, following the manufacturer's instructions for drying times.
5. Sand lightly between coats for a smooth finish.
6. Apply multiple thin coats rather than one thick coat for better durability.
7. Allow the final coat to cure fully before using the surface.