Reading groups can be single sex or coed and may vary in size. Then meet informally over lunch or dinner to discuss it. Once you've assembled a group or joined an existing one, you're ready to begin. The books are the most important part of the meeting. There are many ways to go about it.
Some groups prefer to take turns choosing what to read.
This way everyone gets to read a favorite. Or, you can leave it up to the discussion leader to choose. Themed discussions not only help you to choose your titles, but they provide natural points of comparison and discussion. Or focus on a specific subject or historical figure. You may find, for instance, that two biographies on the same person reveal very different aspects of that person's life.