If you were a program director (PD), you'd be trying to avoid two big headaches as you assessed a residency candidate:
First, a PD doesn't want to field complaints from patients, faculty, or other services about his/her residents. Therefore, every far-seeing PD asks him/herself the simple question: Will this person be competent and collegial?Second, a PD doesn't want to see the day when s/he's scurrying around to fill a residency slot and the consequent open call schedule. So, the oracular PD asks the simple question: Will this person leave the program prematurely?
As you approach your interviews, consider how you can demonstrate your competence and collegiality, as well as your commitment to the field and the residency program. For the former, ensure you showcase academic successes, extracurricular activities that demonstrate teamwork, and - if asked - hobbies and reading materials that demonstrate your personality. For the latter, highlight research projects in the specialty, sub-internships, and knowledge about the program and city.
Just making sure the PD knows you are not going to cause him/her pain is half the battle.