How can I refinish polyurethane furniture to restore its original shine and appearance?

To refinish polyurethane furniture and restore its shine and appearance, follow these steps:

1. Clean the furniture thoroughly with a mild detergent and water to remove dirt and grime.
2. Sand the surface lightly with fine-grit sandpaper to remove any existing finish and smooth out imperfections.
3. Apply a coat of polyurethane finish using a brush or cloth, following the manufacturer's instructions.
4. Allow the finish to dry completely before lightly sanding again and applying additional coats as needed.
5. Once the desired shine is achieved, allow the furniture to dry completely before using it.