Major challenges in conducting a successful reference interview

Read : Introduction to Reference and Information Services; Determining the Question [Cassell and Hiremath Chps. 1 and 2]. Based on your reading in Cassell and Hiremath Chapter 2 and your own ideas of what is necessary, what do you think are the major challenges in conducting a successful reference interview, and how would you meet those challenges (or how have you met them in the past if you have worked on a reference desk or in a similar capacity)?