I know your interview already happened, but there are several things to consider in the future (assuming you will have to interview again eventually). One way to become a master interviewer is by standing in front of the mirror. Your posture (or sitting) greatly determines how the interviewer views your interest. It may seem silly but it's good practice. Look engaged, lean forward, smile, and always ask questions. Remember, you're interviewing them at the same time. You want this to be a good fit. Hope this helps.