Some tips for repairing door locks at home include making sure the door's latch bolt lines up with the doorjamb's strike plate, tightening the doorknob by loosening the setscrew on the knob’s shank and turning the loose knob clockwise, and using a bottle of lock de-icer to lubricate slow-working locks. Fortunately, these actions can all be performed fairly easily without professional help.
If the door latch doesn't operate as smoothly as it should, it is possible that the door's latch bolt may not be properly lined up with the doorjamb's strike plate. Close the door slowly to watch how the latch bolt meets the strike plate. If the latch cannot reach the strike plate, shim out the plate, or add another strike plate if necessary. To adjust for a small misalignment, file the inside edges of the plate to enlarge the opening.
For a loose doorknob, simply loosen the setscrew on the knob’s shank, and hold the knob on the other side of the door. Then turn the loose knob clockwise until the fit is sufficiently tight. If this does not work, it may be a good idea to remove the knob and check the spindle to see if it has worn down to the point where it needs to be replaced. If the door lock works too slowly, a bottle of lock de-icer contains alcohol and other lubricants that can dissolve dirty, sticky deposits.