Reservations?

We are ready to embark on our full-timing adventures starting in July. I have followed this forum as well as many other blogs over the years and find that many people do not make advanced reservations. Coming from the Northeast and being primarily weekend and short vacation campers until now going without reservations has my wife very nervous. Are there rules of thumb on when to make reservations and when to wing it? Your advice would be appreciated.

Mark and Catherine