Interview tips for competition?

I think of myself as fairly good at interviews in general, and input from people who have interviewed me agrees with this view. My style is pretty laid back,I do dress up, but I don’t really follow strict “interview rules” I tend to smile a lot, answer questions quickly (or if I don’t have a quick answer I say “that’s a tough one” to stall for time). The thing is, I’m entering an interview competition (it’s for academic decathlon), and I’m wondering, what should I change for competition. It really seems totally different to me, when I’m interviewing for real I’m trying to tell the interviewers, “I’m someone you want to work with” and I don’t really want them to think I’m particularly “good” at interview, after all why would you hire someone just because you thought they were good at interviews?

It just seems really weird to me going into an interview trying to convince someone I’m good at interviews, any tips?