Just want to say for us when we randomly took our first cruise last year we got a GVT where it was a guaranteed verandah and saved like $1000 off opening day. You have to be completely okay with whatever you get and be prepared to not be able to know which room you have until you show up the day of.
If you have your heart set on something though book it early because we picked the cruise because it was so much cheaper and have complete flexibility when we would cruise.
I am thinking this time just booking this Friday when I can (DVC and Silver booking day).