Interviews seldom offer the chance to say anything worth hearing, no matter how well-prepared the interviewer. You are invited to rehash your material, saying it again in worse words. "What did you mean when you said....?" etc. Or "Why did you write this book?" It isn't enough to say that you wrote it because it's your job and you thought readers would like it.
I once heard Salman Rushdie in discussion on stage in St Louis, and he said that there's only one question to ask an author. You point to a sentence, and say, "How did that get there?" Then a tale unfolds, the book's hinterland. You get to see the shadows moving behind the substance.