I found this picture and informative text on the website of a security consulting firm based in Canada:

Become familiar with your handcuffs. They can be your best friend or your worst nightmare. Ensure that they are in good operating condition: Check for binding between the single and double strand. Check for rust in the rivet. Ensure that the lock and double lock mechanism work properly. Feel how much pressure is required to unlock your handcuffs. Ensure your pouch is accessible and the cuffs are not double locked when stored.

Good advice, if you ask me!