All the time and effort you put into producing a professional/polished résumé should be complemented with a well constructed cover letter. When receiving a letter and résumé, most employers will read the letter first. This means that if you want an employer to give your resume serious consideration, you have to sell yourself in your letter.
Writing effective letters takes considerable thought and effort. You must reflect not only on your personal objectives, but also on the needs and interests of your reader and the requirements of the situation. Ideally your letters should flow from and be linked to the following career development activities:
Even though letter writing most directly supports the last three tasks, it is important to place this activity in the broader context of career planning and your job search. Should you find yourself struggling with your letters, it may be because you have failed to devote the necessary attention to assessing your strengths, researching occupations and employers, and defining your work objectives and career goals.