When I start my book clubs, I devote A LOT of time to it, so my students can get into the routine. As stated in my earlier post, I allow my students to choose their own groups (typically 4 because that's how many copies I try to buy of my books) and select whatever books they want to read. I know this part is hard for a lot of teachers because you have to let go of control, but I really think it's one of the most motivating factors of book clubs. Students really appreciate having complete control over what they read. (Although... you have some say since you're the one, for the most part, providing the texts.)
My students set their own reading schedules, so they are able to read at a pace that works for them. Each group filled out a bookmark where they recorded their next meeting date and reading target (either page number or chapter everyone agreed to meet). Once again, I am more concerned with making sure every student is reading consistently and let go of the control over pacing. For the most part, this works itself out because students are anxious to get to their next book choice.
In the beginning, I give my students one period (about 40 minutes) to work on their book clubs each day. They typically spread out around my room (under desks, on top of desks, whatever… I don't care as long as they're reading. My only rule is that they should be able to put their arms out and turn in a circle without hitting anyone else (to keep chatting to a minimum).
During this time, I typically meet with two groups (20 minutes each). Each student in the group was assigned a role, similar to literature circles. I gave them completion grades for these each time I met with the group because it was their accountability, but I didn't make them actually stick to their roles during discussion time because I wanted their discussions to be authentic. Still, I think having roles (especially for younger students) gives students a good starting point because it forces them to prepare something for the discussion.
In the beginning, my students needed more guidance from me about how to keep a conversation going for a full 20 minutes, but after a couple weeks, I was able to sit completely back and just listen to them. It was very easy to see who was reading (and by FAR, most of them were), and I only had to chime in when they weren't digging deep enough.
We did a lot of work with the types of questions we were asking and how to thoughtfully respond to each other's ideas instead of just throwing out new questions after one person responds. For each group, we set goals together related to their reading and discussion skills, and I took annecdotal notes during their discussion days to record the progress.
I will admit that I was concerned, at first, about how this would work with varying reading abilities, but it actually worked out well. I think they were more motivated to push themselves because they had so much choice and wanted to read what their peers were reading. I wasn't so much worried about the levels of the books (although they were all reading books from my library, so I knew the range was appropriate) because I was more interested in making sure they were invested in reading.
My students LOVED book clubs. We did it consistently for 2 months (while I used my other period to focus on writing prompts) and then had to take a break to do a district-required novel study. They were SO mad and begged to bring it back after the novel study. At Family Math Night one year, a mom asked me what I did to her son because she couldn't believe that she found him in his room reading for pleasure. It was music to my ears!!
For the sake of time, I tried to continue the book clubs without having the groups meet with me (I would teach a small group during this time instead), but I don't think the investment was there. They wanted to be able to share with me all the things they were thinking about their reading. Although I never tried it, you certainly could have all your groups meet on the same day (so you don't have to worry about distractions from the conversations) and monitor the rest of the students as you would during a reading workshop.
Speaking of reading workshop, you may want to consider adding book clubs as an option during this time. If students prefer to read independently, allow them to keep doing so, but maybe you can offer this to those who may benefit from the positive peer-pressure of a book club. They really are a really great way to motivate my reluctant readers AND my reluctant talkers. In groups of four, no one can hide in the background, and they all felt more willing to share their ideas since they were among friends.
As always, if you have further questions, please don't hesitate to leave me a comment. I always try to respond via email to open up that method of communication for when you have follow-up questions or comments as well.