How do you begin to plan for extended road trips?

Last year was the first time I did any planning. I traveled for 4 months and I made a single reservation for 4 nights in Arches NP. The campground in Arches is usually booked well in advance and it had been years since I was able to stay for more than a night or two.

Otherwise, I usually have some vague idea of the National Parks and areas I want to see. It also makes it easy since I rarely stay in RV parks and I do not need hook ups.