Tie one end of the thread to the shaft of the paper-clip inside the matchbox. Make sure that it's pulled tight, and then add a dab of glue to secure it.

Straighten the second paper-clip and bend it to form a hook shape. Tie the hook to the loose end of the thread.

Attach a small piece of plasticine just above the hook. This will act as a weight and help the crane run smoothly.