To refinish a wooden door, remove the door from the door frame, take the hardware off the door, and lay it flat between two padded sawhorses. Sand the door to remove the old finish, and remove the dust. Reattach the door hardware, and hang the door after applying sealant to the top and bottom of the door. Stain the door, and apply a polyurethane topcoat, or apply primer and paint the door.
Use 80-grit sandpaper to remove the old finish, and resand the door with 100-grit sandpaper. Sand the door a third time with 120-grit sandpaper until the wood is smooth and the remaining finish is removed. To remove the finish from moldings or other recessed or raised features, use a teardrop-shaped scraper, and follow the grain of the wood. Use a sanding sponge to remove finish inside corners or other small spaces.
Apply stain or paint to the door after it is hung to simplify finishing the door, or apply stain, paint or top coat to one side of the door and allow it to dry completely before flipping the door to finish the second side. Allow both sides the door to dry completely before reattaching it to the door frame.