Working the challenge: well, it for you, really. You just set a goal and then report in periodically on how you're doing
My goal is going to be 50 books from here between September and Christmas (I want to finish my summer challenge first). Your goal could be some other amount/timeline. As long as it's about books from here, it's on-topic.
For my other 'main hobby with huge message board' (collecting/using fitness dvds) we have all sorts of check-ins and challenges. Some are more specific (people using a specific set or instructor) and some are more general. But I find when I join one, I enjoy the camaraderie of others doing the same type of thing. So I announced my summer reading goal, and while it did not take off into a huge thing, necessarily, there are a few others checking in from time to time, and I enjoy that.