When is the best time to book?

I am planning a vacation to Sanibel Island, and I am just looking into when we should take our trip, and how far in advance we need to make the hotel and airfare bookings in order to get the best deal. When is the best time to book Sanibel Island hotels? When can we get the best deals, and how far in advance is it necessary to book the hotel in order to get these deals? Is there a busy season and a slow season? And would we still have fun in the slow season or does everything kind of shut down?