To winterize a wooden garage door, start by inspecting the door for any signs of damage or wear, such as cracks or holes, and repair these as necessary. Apply a fresh coat of paint or stain to protect the wood from moisture. Check the weatherstripping around the door and replace it if it's worn or damaged. Lubricate the door's moving parts to ensure smooth operation. Finally, consider adding insulation to the door if it's not already insulated. This can help to keep your garage warmer during the winter months.