To fix a door lock that doesn’t turn easily:
- Squirt a little powdered graphite (available in squeeze tubes at home improvement and automotive stores) in the keyhole of the lock.
- Insert the key in the lock and turn it several times to distribute the graphite.
In a pinch you can rub lead from a soft pencil (which is composed of graphite) on the key, then work it back and forth in the lock. Be sure the lead in the pencil is made from true graphite.