You don't get a second chance at first impressions — especially when it comes to cover letters.

The purpose of most cover letters is to sell yourself to a stranger, so they’re really sales letters. Think of your cover letter as a form of direct mail, and craft your letter using these eight rules direct mail experts use:

1. Open with a bang.

This is the line I used to write: "I am writing to apply for the position you advertised … blah, blah, blah." Of course you are writing to get a job! Instead, use your first line to sell yourself and make yourself stand out. For example, instead try, "I think your company can use my exceptional sales skills and 10 years of experience in your industry."

2. Be clear and concise about your purpose.

Your cover letter is the introduction to your résumé. If your cover letter is longer than a page, it is likely longer than your résumé, and who ever heard of an introduction that is longer than the main event? Also, write a separate letter for each job you apply for, because each cover letter should be specifically relevant to the position.

3. Use your time wisely.

A hiring manager spends about 10 seconds looking at a résumé to decide whether to reject it. That time includes your cover letter. Every line of your résumé should sell you to your prospective employer. You never know which sentence will catch the reader's eye. This is true of the cover letter, too. In fact, it's shorter, so it should sell with more punch.

4. Format strategically.

Bullets work well in a cover letter to highlight your relevant achievements. Odd numbers of bullets are easier to read than even numbers, so use either three or five. Seven is too many — the list will look so long that people will skip it.

5. Tell the reader the next step.

A cover letter introduces a résumé, and the function of the résumé is to get an interview. So in the cover letter ask the company to call or e-mail you to set up an interview. This call to action makes a nice last paragraph.

6. Say it, and then say it again.

Put your e-mail address and phone number at the top and bottom of the letter. The hiring manager should not have to hunt for your contact information.

7. Come back to it.

If you are using a form letter and end up with the wrong company name in your opening sentence, your computer’s spell-check won't catch it and you probably won’t either, because it's hard to edit something you’ve been rewriting for an hour. Come back to the letter in two hours, proofread it, and then send it. You'll be amazed at the errors you catch — and grateful you took the extra time to check.

8. Follow up.

You have to call. You might not get through to a real person (and if you do, there’s no guarantee he or she will give you any information), but there is a chance that someone will take a look at your résumé just because you called. Besides, picking up the phone is a lot easier than finding another job opening and writing another cover letter.

Penelope Trunk has launched new businesses for multinational corporations and founded two companies. Her writing has appeared in the London Times, the LA Weekly, and Time magazine online, among other publications.