A professional cover letter increases the number of interviews received.
Well-written cover letters make the applicant stand out by showcasing particular strengths, and can be customized to match individual job descriptions.
Professional cover letters match the tone and style of the resume; indicate that the applicant has vast experience of professional business practices, and a proven track record of success.
What makes a Good Cover Letter?
Address it to the person who can hire you. Resumes sent to the personnel department have a tougher time of it. If you can find out (through networking and researching) exactly who is making the hiring decision, address the letter to that person. Be sure the name is spelled correctly and the title is correct. A touch of formality is good too: address the person as "Mr.," "Ms.," "Mrs.," "Miss," "Dr.," or "Professor." (Yes, life is complicated.)
Write it in your own words so that it sounds like you--not like something out of a book. (Electra gets in trouble with libraries when she says things like this.) Employers are looking for knowledge, enthusiasm, focus.
Being "natural" makes many people nervous. And then even more nervous because they are trying to avoid spelling errors and grammatical mistakes. If you need a little help with grammar (do they still teach grammar?)--check out the classic work on simple writing, Strunk & White's Elements of Style, published in 1918 and now online. A good place to begin is "Chapter 5: Words and Expressions Commonly Misused."
Show that you know something about the company and the industry. This is where your research comes in. Don't go overboard--just make it clear that you didn't pick this company out of the phone book. You know who they are, what they do and you have chosen them!
Use terms and phrases that are meaningful to the employer. (This is where your industry research and networking come in.) If you are applying for an advertised position, use the requirements in the ad and put them in BOLD type. For example: the ad says--
"2 years' experience processing magnetic media (cartridge, tape, disc); interface with benefit plan design, contracts and claims; and business background with strong analytical & technical skills--dBase, Excel, R&R, SQL."
Make sure your cover letter contains each of these requirements and shows how you measure up.