I had a meeting today with a group looking to collect some oral histories from its pioneer members. I told them about a video from Traditional Arts Indiana about getting interesting answers from your informants.
You can watch the video here:
In the same series is this video on structuring interview questions.
I like the topics-based approach taken in this second guide, where the suggestion is that an interview ask questions based on five topics: beginnings; community; aesthetics; process; and, creativity/traditionality. It is a good idea for people doing any kind of folklore interview related to traditional and contemporary craft or practice.