One more thing. Unless you have a particular tasting or time that you just HAVE TO HAVE, I recommend not going to guest services or the other sign up location right away.
That first afternoon (and the final evening) are the busiest times at guest services. If you just wait until later in the day, or the second day, there will still be plenty of choices and no lines. My wife stopped by the bar that had the signup book on the morning after embarkation, and they basically handed her the whole list and let her browse and text us, etc. as much as she wanted. No lines. No rush. When she was ready, they took down all of her requests.