Go to direct-mail school in your mailbox. If you're like most Americans, each day your mail brings you a handful of direct-mail solicitations that you can use as your hands-on education. Study the letters. Use design ideas from the fliers. Keep copies of different types of reply cards. Big-time direct-mail companies spend millions refining their mailing techniques. You can use that information for the price of tearing open the envelope. A real bargain.