Be patient with him. Find which hand he is most comfortable with and let him use that hand. If his name is "John" when he's practicing his "J's" let him practice with his finger first, (write the J in the air), then give him the pencil or crayon, and let him practice with that in the air (example: start at the top, go down, make a hook, and put a hat on top) Keep practicing that way, then have him do it a couple of times on paper. Once he's mastered the first letter practice on the next and so on. Or, if you can write the alphabet in large letters for him, and have him trace the letters with his fingers first, and then have him practice writing them. Find some shapes that you can associate with his name, and let him draw or trace those shapes, and then have him practice his name.