I started one up about five years ago, and we're still going strong. We meet once a month on the last friday of the month. That way, everyone knows when it is, and can put in their diaries in advance.
We have run it two ways:
Initally, at the start of the year, we all put details of two books we wanted to read into a hat, and they were drawn out randomly. We picked 2 books each month, and people could read one or the other or both. The advantage of this method was that if you didn't fancy one of the books, there was another to read. The disadvantages were that it was too set in stone - there was no scope to read a newly released book, for example. It was also divisive - when people were talking about the book that they'd not read, people lost interest.
So now, we all choose one a month, but the list of who's chosing when is decided at the start of the year. This means everyone knows when their turn to choose is, and they have time to think about it. We choose two months in advance - ie, I chose in March for the book we discussed in May. This gives people enough time to order the book from Amazon or the library.
We have no rules about the types of books that can be chosen (apart from no hardbacks).
We talk about the book at the beginning of the night (before we've drunk too much wine!) and then we mark it out of 10. I keep a book with the scores.
Your local library - if you still have one! - may provide you with a list of books that they have multiple copies of. Mine was really helpful, and gave me a separate ticket and let us keep books for six weeks and don't fine us for late returns.
Hope this helps. Good luck.