A cover letter is also a marketing document and provides an opportunity to really show how your experience matches up with the job.

It should be short, concise and loaded with quantifiable info that links your experience to their needs.  Major points of info should be bulleted, not in narrative form.

Always remember to thank them for their time and consideration.

Always remember to ask for the opportunity to talk and drill down into what it is they really need; confident that you can meet that need.