A cover letter should always be included when submitting a resume as it allows the applicant to expand on their qualifications and highlight relevant experiences. An effective cover letter is short, getting straight to the point in three paragraphs - an introduction stating the position and how you learned of it, why you are interested, a middle paragraph marketing your skills and qualifications with examples, and a closing thanking them and stating your contact information and intent to follow up. Cover letters provide additional context beyond what is in a resume to showcase why an applicant is the best candidate for a job.