I've sat in on countless interviews very similar to the one you're facing, and for me, the things that set quality interviewees apart are honesty and preparation. Honesty comes through--it's not hard to spot someone who doesn't know what they're talking about and is attempting to cover for it. It's also easy to spot someone who isn't sincere in their answers. So be honest. If you have areas where you'd like to improve, say so. It also helps to be able to speak in an informed manner about the position you're trying to get. Speak in specific terms. Don't just say you'll do a good job, give specific examples and how you would handle them. It also helps to be able to come up with specific examples of what you've done in the past that would make you a good leader.