Also try looking at reviews when you're done. Not the simple ones that just said "I hate this book!" or "This is the best book ever!" or people who simply relate the plot, but hunt for people who detail what they do and don't like and why or give interpretations of the text. Those reviews provide a lot of discussion fodder.

Reviews aren't explicit questions but thinking about why their like/dislike is valid/invalid can be rather thought provoking.

Reviewers that agree with you might be able to crystallize something that you enjoyed about the book but didn't have the ability/knowledge to verbalize. Reviewers that disagree with you might be able to provide more cultural/literary context to consider. You don't have to agree with anyone on the reasons a book is good/bad but just try to keep an open mind. Just because you adored a book doesn't mean a guy who hated it is wrong in his criticism - he might just care more about particular aspects than you and give it more weight when forming his opinion. And vice versa.

You can also hunt for online book clubs that discuss your book, but those can be pretty hit or miss, IMO. Some just tend to post reviews and not discuss, and others tend to just declare proudly that they finished. It can be difficult to find the ones that actually discuss books in detail.