When you need to start a nail in a place that's just slightly out of your reach, try this carpenter's trick: Insert the nail between the two hooks that form the hammer's claw. Be sure the nail head is resting against the base of the hammer head and that the nail shaft is wedged into the claw.
To start the nail, hold the hammer backward — with the striking face toward you — and firmly swing the hammer to drive the nail point into the workpiece.
Turn the hammer around and drive the nail all the way in. Note that this technique only works with curved-claw hammers, not straight-claw framing hammers.