Ask open ended questions – avoid questions that only require a yes or no answer.
Prompt for more details - if your interviewee does respond with short answers, use phrases such as "What was that like?", "Tell me more about that...", to get them to elaborate.
Active listening - be present, nod, smile, and make eye-contact. Try to avoid "Uh-huh" and audible interjections while your interviewee is talking.
Make the most of sound check - while you are checking your audio levels, use this time to get the interviewee to open up. Ask easy questions like "What did you have for breakfast?", "What is a typical day like for you?", "Are you a morning person?" Look for opportunities to connect.
Have an interview outline - you don't want to necessarily read from a script but it is a good idea to have your questions or topics on a notepad with you.
Don't be afraid to go off-script - if an interviewee brings up something unexpected, go with it. At best, it may end up being something interesting you hadn't thought of, at worst you can always edit it out of the final podcast.
Prepare your listener - You can always front-load your podcast with an introduction and/or short biography of the interviewee. This way the listener comes to the interview with a framework and context for the interview. It also helps you get to a more natural conversation with the interviewee if they don't have to go over their life story/resume.
Unsure what to keep and what to cut from your interview? Read this helpful article from NPR.