Sand the entire door with 180-grit sandpaper until the wood surface is completely smooth. Always sand in the same direction as the wood grain.
Clean the door with a tack cloth to remove dust from sanding.
Tape off any areas of the door that you do not want stained, such as hardware, using painter's tape.
Prepare a mixture of liquid dish soap and warm water in a bucket in the same manner as you would prepare a sink to wash dishes.
Wash the door thoroughly with a cloth rag and soapy water.
Rinse off the soapy water to remove all soap residue.
Dry the door off with a clean rag. Allow the door to dry thoroughly.
Use painter's tape to tape off any areas of the door that you don't want to stain.