I too have periods of time when I'm not on the site as much as other times but I love the group reads and have perfected this method for making sure I don't miss out on them. I once missed one when the GRs were done kind of randomly but now the novels are done twice a year, once in the spring and fall in the order the novels were written so it's pretty easy to predict a general start time. I always make sure I know which novel is next. If I forget I look it up on the FAQ page or from the library page (Emma is next btw). In March I begin checking at least once a week or so and the same around August. It is always, without fail, announced on the Site Announcements page as Kathleen said which is located in the upper left hand corner at the bottom of the listings under the Pemberley icon. It is also always announced on the novel board of whichever novel is next in the cycle. As you may know a week or two before the GR starts, there is usually a thread where you can say what your focus will be or if you are a newbie.

Sometimes other GRs come up like the letters, or other related texts so I continue to check out the announcement board so I can participate if I wish.