What's the best way to align hinges?

Installing a long piano hinge generally frustrates me. Surely there's a simple, surefire method that will ensure the hinged parts are aligned so the surfaces of both pieces are level with each other. Got any suggestions?
—Charles Cottingham, Columbia, Missouri

The hinge itself can solve your alignment problems, Charles. To start, mark both workpieces where one end of the hinge will be located. Then open the hinge so its barrel is on the outside of an L formed by the two leaves. Lay the hinge on a workpiece with one end against your hinge-end mark and a leaf resting along the edge, as shown above. Press the other leaf flat against the top surface and clamp the hinge firmly in place. Place the tip of a self-centering Vix drill bit in the hinge leaf holes, and drill pilot holes at each screw location. Move the hinge to the other workpiece where it will later be mounted, and repeat the process. This way, the two outside surfaces mount level with each other, and the hinge barrel rides at a uniform height between both parts.