Beings you are a beginning snowbird, I'm going to recommend you do what I did. When I decided to do the snowbird thing I spent a season checking out each snowbird area. I did one season in Florida, one season in south Texas and a season in the Southwest.
I never stayed over a month in any particular RV resort or campground, usually only a week or two and moved on the the next area. Had a great time doing this and it gives you the opportunity to see what suits your needs.
I never did any reservations, and still don't. If you are not particular and are not looking to stay in a definate place for a definate amount of time, reservations are not necessary. There is always some place to stay.