1) Using the wrong list. Perhaps the biggest mistake that you can make is to use a mailing list that does not represent your target audience. Too many people send out mailings, receive no response, and wonder why. Make sure that your list is current and targeted to meet your needs.

2) Poor copy. It may only be 100 or even 25 words, but they need to be the right words. Take the time to do several rewrites until the copy will grab the reader’s attention.

3) No call to action. If you don’t tell the reader what you want them to do, it defeats the point of sending the direct mail piece. Do you want them to call you? Email you? Send in the enclosed postcard? Buy something? Make it clear what they should do or they will not respond.

4) No testing. Too many people learn the hard way that their direct mail piece is not effective. It should be common practice to test out anything you plan to use to market or advertise your business in order to see if it makes an impact.

5) Using hype over meat. It is all too common to hype your product or service with superlatives instead of highlighting and explaining the actual benefits of your product or service.

6) Not proofing the copy. There are too many stories of great direct marketing pieces that were missing phone numbers, addresses, or other key information. Errors in the copy are also too prevalent. Proofreading is an important aspect of all of your marketing campaigns. If you feel that you are lacking in those skills, hire someone to proof your copy. Or ask a colleague who has a way with words to take a look at your text.

7) Not focusing on your headline. One of the reasons we all toss direct mail quickly is because it does not grab us. Somewhere between boring headlines and gimmicks is a smart use of a headline that catches someone’s eye without insulting their intelligence. You only have a few seconds to grab the reader, therefore you need to put great stock into your headline.

8) Highlighting form over function. One common mistake is placing too much focus on the design elements of the direct mailing piece, which results in marvelous four-color graphics, interesting shapes, and eye-catching color, but a discrediting loss of content.

9) No follow up. Many businesses send out brochures, fliers, and other materials with no follow-up plan. Follow-up refers to calling, mailing additional information, or at least being prepared to fulfill requests for the product or for additional information.

10) Not tapping into expert advice. Direct mailing has been around for many years because when it works it works very well. Many people have spent their careers mastering the art of direct mailing. They know the right words to use and the best ways to get results. However, far too few people tap into this bank of knowledge. Do your research and learn from experts in the field.

This information is taken from All Business (dot) com

http://www.allbusiness.com/marketing/direct-marketing-direct-mail/3986-1.html