First, remove the stripped screw, either with a screwdriver or a good set of pliers. Next, squirt some carpenter's glue into the hole, insert the pointed end of a golf tee in, and tap the tee into place with a hammer. Using a sharp utility knife, cut off the exposed extra part of the golf tee so that it's flush with the door frame. This will give you a fresh piece of material to drill a new screw into.