Obtain a key for professional handcuffs from a favorite army surplus store or locksmith. Because they are designed to restrain a prisoner under supervision and not actually to serve as a locking device, most professional handcuffs use the same key out of convenience.
Purchase different styles of handcuffs commonly used such as traditional police style handcuffs and the hinged cuffs favored by many military groups.
Practice unlocking the different styles of professional handcuffs while restrained. Many handcuffs have enough slack to allow one hand to unlock the opposite cuff while others will require holding the key with one's mouth.
Learn to hide the key in clothing or in the area of the performance and practice retrieving the key while restrained. Houdini is even said to at times have hidden a key in his think hair.
Plan for emergencies by hiding more than one key in the performance area. A tactic used by many escape artists dating back to the days of Houdini is having a confederate slip the performer a key during a last minute good luck handshake.