Buff and polish hook if damaged. Inspect needle plate. Remove needle strikes, make sure plate is straight. Check needle positions, height, relationship to hook and needle plate, left and right, front to back. Check pendulum timing.
Check feed dogs, height, alignment, and timing.
Check presser foot height, and alignment. Check function of pattern mechanism. Test sew on machine. Adjust tensions as needed, check spring, tension release, etc. Check bobbin winding mechanism.