Use paint remover to take off any paint that doesn't give a rustic feel. Sand away any glossy finishes carefully.
Rub the surface of the door with steel wool to further distress its appearance. Rub only with enough pressure to create small nicks.
Choose a rustic color for the door, such as a muted brown or antique white. Apply the paint or stain as per the manufacturer's instructions, and allow it to dry. Sand the surface lightly for an uneven look.
Add vintage hardware to the door, or distress the existing finishes. Use sandpaper to instantly age the pieces.