The best cover letters are those written specifically for the job -- cover letters that generally list the applicant's skills and accomplishments without explaining how they relate to the company's open position and overall success will not be effective. According to the JobStar website, some companies may even interpret such letters as a sign of laziness. Consequently the best cover letters must demonstrate research into the organization as well as excellent formatting and editing.
Write your name, address, phone number and e-mail address at the top of all cover letters. Follow this personal information with the date of composition. At this point you need to conduct research into the company, because you should include the name and address of the person you're addressing in the letter, as well as a formal invocation such as "Dear Ms. Smith." If you didn't receive instructions on whom to address in the letter, search for the name of the hiring director or human resources director. Avoid impersonal forms of address like "to whom it may concern" -- these invocations appear too formal.
The opening paragraph needs to grab the reader's attention -- hiring directors read large numbers of cover letters for every position, and the best cover letter will differentiate you from the crowd. Avoid explaining how you heard about the job opening. Instead, briefly state which job you're applying for and then explain why you are interested in working for the company.
The body paragraphs of your cover letter should reinforce your qualifications for the job. Because most applicants will have similar educational and professional backgrounds, cover letters that emphasize specific accomplishments and events will be the most effective. Instead of simply stating that you have a relevant degree, for example, discuss a moment when your education helped you solved a problem and then explain how that situation prepared you for a position in the company.
Like the introduction, the conclusion should be brief. Thank the readers for their time, mention the enclosed resume and request an interview to further explain your qualifications. If you can mail or fax the cover letter with your hand-written signature, doing so will increase its appearance of professionalism.