The document discusses common mistakes that job seekers make in their cover letters that can lead to rejection, such as using an irrelevant format or template, including grammatical and spelling errors, making the letter too personal or lengthy, making unsupported claims, listing irrelevant skills, sending a generic letter, and failing to address the recipient. It provides tips for writing an effective cover letter, such as customizing each letter for the specific role and company, keeping the letter to one page or less, and directly addressing the hiring manager.