Doing an interview you're going to have certain things you want to get at, but you're better off if you play to people's strengths a bit. You're also assessing how it's going and adjusting as needed. Does your subject seem up for it, willing to do it, and is he or she enjoying the interview? Or do they need to be coaxed, or reassured, or whatever they might need from you? Like writing, interviewing is a process that you keep learning, and you're always trying to get better and better.