Use a stud finder to find the stud in the wall. Studs are the wooden supports that hold up the frame of the wall at even intervals. Mark the stud with a pencil about 6 or 7 feet from the ground -- the recommend hanging height for the clock for maximum running time.
Hammer the nail into the mark you made in step one. Hammer the nail in at an angle so that the nail is tilted slightly toward the ceiling. Leave at least 1 inch of the nail protruding from the wall.
Hang the cuckoo clock on the nail via the hole in the back of the cuckoo clock. If it does not rest flush on the wall, hammer the nail in slightly farther.