Hiring managers typically use your résumé to determine whether you're qualified for the job, and the interview to decide if you're the perfect fit.
Knowing that, most people take the process very seriously. They arrive to the interview on time, dress impeccably, and answer each question intelligently.
But as it turns out, there's more to it than just showing up and doing your best - there are dozens of small details that overtly or subconsciously affect the way you're perceived.