During the tribute to Tim Russert on Sunday's "Meet the Press," that's what James Carville said he told politicos who were going to be on the show. But his advice applies to anyone (authors included) who's going to be interviewed, whether it's on TV, radio, in print or in public.
If the interview is worth your time, it's worth taking seriously. Know the show/publication/venue and be familiar with the interviewer. Know what you want--and DON'T WANT--to say.
Be a pro: be prepared, not frivolous.