The Purpose of Your Cover Letter
Your cover letter is meant to augment your résumé. It should not simply restate what your résumé already states. In fact, if crafted properly, your cover letter should provide a reason for the prospective employer to look more closely at and regard with more credibility your résumé.
In your cover letter, you are attempting to demonstrate how the skills and experience in your résumé are part of a larger, more complete picture. Not only do you have value and skill, but you also have a professional attitude that will benefit this company. In effect, your cover letter serves as a bridge between your résumé and a specific opportunity.
Your cover letter also provides a place for you to do a little bragging. Remember the adage, "If you don't toot your own horn, nobody will." This is certainly true, but you must handle it with tact.
Some might disagree, but I am a big believer in self-promotion. Proclaiming your successes can work to convey a sense of pride in what you do. Although you do not want to appear arrogant or conceited, confidence in your ability to achieve can go a long way toward helping a potential employer become comfortable with you.
Every time an employer hires someone, he is taking a chance. During the hiring process, from the initial contact with your cover letter and résumé, and through the interviews, you must work to make the employer believe that giving you a job is a good idea. The employer will not get to that point unless he is confident that you can do the job.
Your own confidence helps the employer gain confidence. Imagine a prospective employee being asked why hiring him would be better than hiring the next guy. If you are the prospective employee in this case, it would serve you well to have an answer that exudes confidence.
Remember the first tool in your toolkit—the attitude that you have something valuable to offer. Your cover letter is the first place where you get to use that tool.