One of the most common questions my copywriting clients ask me when doing direct mail is which format is best – a postcard, self-mailer, or sales letter?

Here are some guidelines to help you answer that question:

>> When in doubt, go for a sales letter with reply element in a #10 envelope…still the most powerful and proven format.

>> Self-mailers work well when your product is visual (e.g. selling vacation cruises, Christmas lights) and you want the prospect to see pictures right away.

>> Postcards work best when driving response to a website URL or toll-free phone number.

>> Letters in envelopes work best when selling professional or technical services, and with promotions that have an emotional appeal or a story to tell (e.g. life insurance).

Bob Bly is the author of “World’s Best Copywriting Secrets” and has written copy for more than 100 companies including IBM, Boardroom, Medical Economics and AT&T. He is the author of more than 75 books and a columnist for Target Marketing, Early To Rise and The Writer. McGraw-Hill calls him “America’s top copywriter”.