In this case, hand them your resume without a cover letter. If you're sending a resume by mail, if you giving your resume to a friend to hand in, or if you leave your resume with the hiring manager's secretary, you are not shaking the hiring manager's hand and do need to have a cover letter enclosed with your resume. Brief and Simple Hiring managers only glance at cover letters. They have tons of resumes to read and will select a few candidates for interviews. I recommend letters be approximately 3-4 paragraphs.
Many people provide lengthy autobiographies in the cover letter.
They regurgitate their resume and then some. This is a waste of the writer's and the reader's time. If you're perfect for the position, explain why. Include contact information and outline when you're available. Word choice Never underestimate the power of your word choices in the cover letter.