The best advice I ever got with respect to conducting oral histories was to read a bunch first. Pick up a copy of Studs Terkel's Hard Times or Working and thumb through a few stories to get a handle on the types of questions Terkel asks. Hard Times is especially worth your, well, time.

When you conduct your interviews, ask questions that are open ended. "Tell me about . . ." or "What do you think of . . ." are great ways to start a conversation. Take notes about what the interviewee is focusing on, but try not to interrupt the flow of their story. When a pause happens, go back and ask about something they mentioned but did not expand upon.

My great grandmother died in 1982, having lived to be 97. Before she died, she gathered up all of her great-grandkids and talked a bit. I was much too young to think of recording what she said, but the conversation is still a large part of family lore. We talk often of how she described the huge changes she witnessed, and how they made the world smaller and better. Two world wars, the invention of radio, TV, telephone, suburbanization, moves toward gender and racial equality, etc. She saw a lot, much as I'm sure your grandparents have.