Pinch two plates together, smooth sides facing out, gripping them purely with your fingers and thumb rather than letting them rest against your palm. Stand tall and walk at a steady pace, resisting the urge to squeeze your whole hand into a fist around them — there's nothing to wrap around, only friction between your fingertips and the metal. This tends to fail suddenly rather than gradually, so as your grip loosens, set the plates down under control instead of letting them drop. Keep your shoulders level rather than hiking one up to help the grip; that's your forearm and fingers' job alone.