Just wait to book any of the specialty restaurants when you get on the ship. Trust me, if you do it when you get there, there will be plenty of reservations left. If you do it on the web site before the cruise, you have to pay for it, as well as all the excursions. I've been paying for stuff as we get closer so we won't have a big on board expense.
I tried to book the mystery dinner theatre, but I haven't been successful, so I will have to wait until we get on the ship, Since there might be a hurricane and we they may change our ports, I'm waiting also, you just never know :-) Good luck!