The four quick hit items I derived from this book are:
1) First and foremost, seek to establish rapport. If you cannot establish good rapport with the person you're interviewing, then you may find it difficult to get the information you need. In a way, this advice goes toward establishing trust.
2) Establish agenda, objective(s), and bias(es). Before you go into an interview to gather information, you should have a clear agenda and know your objectives. You should then share this information in advance with the interviewee so that they know what to expect. Along the same lines, you should state any biases you bring to do the table, as well as work to determine what biases or agendas they may have. Not knowing their biases can cause misleading information to be given, either intentionally or unintentionally.
3) Keep them talking. The purpose of your interview is to gather information. You can't do this if you're yammering away like an idiot. Use open-ended questions to start things off, and then keep asking follow-ups that encourage the subject to keep talking. If you're not getting enough detail, try different ways to phrase follow-ups such that you can get them to talk at more length and and in more detail.
4) Prepare, prepare, prepare. If you don't know what you're talking about when you go into an interview, then you're setting yourself up for failure. The best way to establish good rapport and to keep people talking is demonstrate yourself as a competent professional. Being unprepared or under-informed can shut some people up (especially techies!). If you're doing a technical interview, you had better know the tech fairly well. At the same time, nobody likes a know-it-all, so don't imply that you know everything. If you did, then you wouldn't need to conduct the interview.
If you're conducting interviews of any sort, I recommend checking this book out.
