So you've got a group of friends who are eager to start a reading group together. The first thing you should decide is when you'll meet.
Most groups find that once a month is ideal.
This should be plenty of time to read almost any reading group selection and still allow your members time for personal reading. Meeting more often might be difficult with today's busy lifestyles, and probably won't allow people to finish the book. If your group does decide to meet this often, you might consider reading your books in sections and only discussing a few chapters at a time. Some groups find that every other month is better for them. If this is the case for your group, you can allow yourself the luxury of picking longer books.