We seldom make reservations with the possible exception of the final destination before returning home. ie: St Augustine SP is booked most of the time. That was our destination site and due to the popularity we made reservation for the time we wanted and/or could get.
We researched a perceived route with potential camping sites noted. Check their availability, if on ReserveAmerica or other sources with as many alternatives as we can find. Note their names, locations, highlights & GPS coordinates. Then head off to happy camping. Then return trip is basically the same routine with trying to find the last site within a couple of hours of home. For some reason the last day/return trip seams the longest to us, so we want a relatively short drive the last day.
Probably won't work for a lot of folks, but does for us. Besides, during the winter months when we don't get out, we plan, research and wish.
Enjoy and wing it!!!