My Heritage Blog has posted an article about 10 tips for interviewing family members. They are more detailed at their site but here is a basic list of the questions. Most of them are common sense.
2. Create a list of questions or topics to cover (seems like that would be covered under prepare).
3. Decide how you will record the Interview.
4. Call ahead.
5. Start with a family photo.
6. Ask open-ended questions.
7. Create part of the family tree together.
8. Lead the Interview.
9. Leave something behind (not your purse but contact info or a photo).
10. Follow-up at home.