1. Show that you know something about the company, but do not try to flatter or exaggerate your interest in the job.

Correct

Incorrect.
Being knowledgeable about their company would demonstrate genuine interest in working there. Being too flattering would make you look desperate and needy, which is unappealing to employers.

2. Base your interest in the job on achievements and activities described in your résumé.

Correct

Incorrect.
Relating your achievements described in your CV to the company on your letter shows that you are consistent and driven.

3. Avoid using adjectives to describe the companies.

Correct

Incorrect.
It would be redundant to describe companies as they know more about themselves than you do!

4. If you have the required qualifications, mention them in the letter. If the job description asks for a person with certain qualities, try to show that you have those qualities indirectly through evidence from your résumé.

Correct

Incorrect.
It is essential to make sure the employers know about the relevant qualities that you can offer to them. Reword your letter in a way that employers can easily see those qualities you mention.

5. Do not exaggerate your talents. Refer to evidence of your talents in your résumé.

Correct

Incorrect.
Exaggerating your qualities in your letter would make you inconsistent with what you wrote on your CV. Employers can also easily spot the exaggeration in the letter.

6. Emphasize benefits to the company, not benefits to you.

Correct

Incorrect.
Employers are most concerned about the well-being and success of the company, so make it about them instead of you.

7. Do not tell the employer what to think or state conditions for accepting the position.

Correct

Incorrect.
You are not in the a position to negotiate the terms yet. Focus on getting the an interview first before you decide to negotiate.

8. Don't repeat yourself or repeat the details which can be found in your résumé.

Correct

Incorrect.
Redundancy adds unnecessary length and fluff to the letter. Try to make the letter as concise as possible as employers often have to deal with a large amount of cover letters.

9. Be sure to spell-check and proofread your letter carefully.

Correct

Incorrect.
Grammatical and spelling mistakes in your letter makes you look clumsy and careless, which will give the employer second thoughts about considering your application.