I found the following tip online at bravenewtraveler.com:

#8 - Be a little annoying
Don’t be afraid to relentlessly revisit a question or topic that you feel hasn’t been properly addressed by the interviewee. Sometimes people need time to warm up to you or a topic, or will respond better if your question is worded differently. Keep trying.

In an article titled “13 Simple Journalist Techniques for Effective Interviews, Sarah Stuteville, a writer for The Common Language Project (commonlanguageproject.net), also advises, “Be a little annoying.”

After conducting my classmate interview with Collin Brooks, I found that I would need more information on a certain issue in his life that would likely be the focus of the article. I had a lot of information on this topic already, but I still felt the need to know more specific details.

Had I brought up the topic more during our first interview, or reworded the questions, he may have been more apt to provide that additional detail without my having to go back to him.

He was very open about this aspect of his life, but initially I was afraid of pushing him too far, or of asking too many personal questions. I also realize now that it is perhaps easier to interview a stranger, or someone that you do not see on a regular basis.