Your sales letter may be filled with prose so beautiful that it would make Robert Frost weep.

But if your sales letter doesn't meet its only objective - to sell your product or service - it's a waste of time and money.

Try these four tips for sales letters that move to your prospects to action.

1. Get the reader involved.

Your letter opening should draw the reader in and make him or her think, "They're talking about me." One way to do this is to place your reader directly into a troublesome situation that he is likely to face - which of course only you can get him out of as a professional automotive retailer.

Another way to involve your reader is to ask a question to which you know the answer will be YES.

Example: Are you having trouble finding a good used car?

Once your reader sees himself in your opening, he'll be compelled to read on.

2. Don't be afraid to go long.

You may feel that your prospects don't have time to read long sales letters. But the fact is, your reader will feel cheated if she doesn't get all the information she wants out of your letter.

Once you pull in readers with your opening hook, they're willing to read the entire letter. So don't sell them short and cheat them of information just to keep it to one page. If you have something to say, say ALL of it.

3. State your benefit.

Your reader is self-centered. He wants to know what's in it for him.

He wants to know that the new color will impress his friends and neighbors, that the low price will leave him enough money for a vacation, and that the option will make him enjoy his new vehicle.

4. P.S. Remember this.

It's well known in sales letter writing circles that after the headline, the P.S. is the most read part of your letter. Readers tend to look at the headline and then drop immediately to the P.S. Use this space to your advantage by including your biggest benefit or call to action in the P.S.

P.S. Mail back the reply card today and get a FREE oil change.

Drawing your prospects in, explaining how your product or service will benefit them and telling them what to do next-these are the elements that separate the killer sales letter from one that's DOA.

Linda Formichelli is a Boston-area freelance writer who has written for more than 60 magazines, including Redbook, Psychology Today, Business Start-Ups and Writer's Digest.