I will come out and admit it – I tend to choose books for my groups by using titles that have reading guides available. Even though 9 times out of 10, the discussion just flows and we don’t even use the questions! I think it’s that I feel the need for a safety net.
If a book doesn’t have them available, a great resource for “generic” book discussion questions can be found at ReadingGroupGuides.com.
They have basic questions for Fiction and for Nonfiction, on a variety of types including Biography, Classics, Current Events & Politics, and Mystery.
Another good source is from LitLovers.com, under their section on How to Lead a Book Discussion. They give some general tips on running and participating in a group, including generic Fiction and Nonfiction questions.