Cover letters are the introduction to the résumé, and recruiters say they want them to be plain Janes. They should introduce you to the company and show excitement for the job, and not much else. In some cases cover letters can be used to explain something inexplicable in the résumé, such as a job gap, says Mark Howorth, senior director of global recruiting for Bain & Co., the business and strategy consulting firm. Howorth adds that they should never be used to brag about yourself. “Cover letters must show that you communicate well,” he says.