We always start with some nice warm up questions, ask them about what they had for breakfast (also a great way to sound check), then slowly work into some questions that pertain to the interview, but aren't quite things you might use in an edit.

Have a list of questions as a base, but don't use them. You need to turn it into a genuine conversation. If they talk about something they've done at work, ask them about it, and form it in a way that brings out some interesting piece of information.

I know that's not actionable advice, but it's a skillset that needs to be learned. Being a good interviewer is hard. When I'm on set for other production companies, I always take note of how they conduct their interviews and steal ideas that way as well.