When preparing for Indie Hackers podcast interviews, Courtland would typically spend a few hours on research: reading about his guests, what they have written, listen to podcast where they have spoken before ...etc. Good preparation could mean a difference between a great and a mediocre interview.
He recommend to plan to ask deeper questions, combining something he wants to know with something the guest is passionate about, thus helping the guest be more energetic and engaged with the answer. The other trick is to position the questions in way that his audience can relate to the most, making them very curious to hear the answer.
Lastly, Courtland says that if you can set your guest with a great intro, that usually goes a long way. Get them excited right from the start, and the energy will follow through the interview.