Lay the blade of a putty knife flush on the deck with the end of the blade nearest the nail head.
Position a nail puller (cat's paw) so that the claw faces the nail head. Angle the nail puller down beneath the nail head. Tap the backside of the nail puller with a hammer until the shank of the nail slides in between the claws of the nail puller.
Pry the nail puller back towards the handle of the putty knife to lift the nail out of the deck board.