The purpose of a cover letter is to introduce your resume, not to repeat everything it says. The cover letter should also give the reader a quick overview of why you are qualified to fill a position.
My strategy is to write a cover letter template after writing the resume. For most people, a template can be used with most resume submissions by simply changing the salutation and job title. Some experts say that you need to talk about the company you want to work for. Unless there is a direction to do so in a job post, I disagree. Most companies want to see how you are qualified. They will address fit and how much you know about the company at an interview.
My model cover letter is four paragraphs long. The first paragraph lists the position being sought, notes that a resume is enclosed, and offers references. Three short sentences. The second pargraph is a summary of qualifications. It is normally five to six sentences and covers key reasons why you will be a good employee. In the third paragraph, I highlight three qualities that fit the positions. These are usually soft skills such as organization, self-motivation, and leadership. In the fourth paragraph, I ask for an interview in these words: This summary cannot fully communicate my potential contribution. I would appreciate the opportunity to speak with you personally and answer your questions.”
A cover letter should be easy to read. It should take less time to read your cover letter than it does to read your resume. Keep it concise, but give your readers enough information that drives them to the resume. That’s the purpose of a cover letter.
Here is a sample cover letter: Sales cover letter