I've been a part of the formation of 2 book clubs.
The first one formed with people I knew well. We informally picked a book to read for our first book club.
The second book club was with people I didn't know, but, who lived in the same geographic area as I did. As these people were perfect strangers, we did not pick a first book. We met the first time to get to know eachother, set the ground rules, and pick our first book. Everyone thought of one book and proposed it to the group.
In both book clubs the rules have been the same.
1. You do not have to have read the book to come to the book club meeting. We did this because life gets busy and sometimes you haven't finished yet. It would be a shame to miss out completely, and, so many times, book club discussions spin onto topics that are not in the book anyway.
2. If you come to a book club meeting and you have not read the book, you must expect that you will hear spoilers. Duh
In both book groups I've pushed for less formality. Other people might want more formality.
In my new book club (the one with strangers) whoever nominates the book that gets chosen has to lead the discussion on that book
My old book club met once every other month. The new one meets monthly.
Hope that helps.
Margaret