Adequate preparation is the key to success.
Familiarizing yourself with the book will build your confidence and help you to keep the discussion going smoothly. The questions you have may be the same ones other readers will have and will want to talk about. Don't feel that you have to defend the author or the book. You want to give people an opportunity to express their opinions, even though you may not agree with those opinions. When someone makes an outrageous statement, don't feel you have to agree or disagree.