Interviews

I am preparing to do an interview (as research) for a novel I started forever ago and finally dusted off. It's been one that is near to my heart, and I don't know why I strayed away from it. I'm a little nervous about doing an interview since I have never really done one for my writing life. I talk to people all day at my full-time job, but it's a little different talking about emotions and life-changing experiences with someone you hardly know.

So...do any of you have any advice for me on what to do or what not to do? I don't want her to feel like I'm grilling her. How do you do your interviews? How long do they last? Do you do them over the phone or in person? Just asking.