A cover letter is the first communication you have with a potential employer, so it's importance should not be under estimated. Unlike a resume, which lists your credentials and experience in a list-like fashion, the cover letter allows you to insert a little bit of personality and attention grabbing information. When in doubt, include a cover letter or your resume and application may not taken into consideration.A Cover Letter Can Set You ApartYour cover letter can almost be thought of as a sales pitch, because it gives you a forum to explain the contents of your resume in a more personable way. You can use the letter to emphasize the most important aspects of your resume, or bring up personal experiences that make you especially qualified but which are not featured in length or at all on your resume. In either case, if all an employer has to go on is your resume, the hiring manager may not be as inclined to call you in for an interview, particularly if other candidates did include one.How to Send a Cover LetterLike a resume, if a cover letter is sent in physical form it should not be folded. Keep your cover letter to one page, and send it along with your resume in an envelope that can accommodate the full sheet of paper unfolded. Place the cover letter on top of the resume, so it the first visible sheet when the envelope is opened. If you transmit a cover letter via email, clearly label the file as your cover letter, or simply include your cover letter in the body of the email.What to IncludeA cover letter should start with an interesting fact about yourself or bold statement about why you are the best candidate for the position. The reason a cover letter can be so effective is that it allows you to really sell yourself in your own words, so grab this chance and run with it. Keep the cover letter short and sweet, only including relevant information that links you and the available job, and don't be dry -- you want someone to remember your cover letter or be enticed to open your resume. On the other hand, don't be unprofessional, and remember that you are communicating with a potential boss or colleague.