How do you begin to plan for extended road trips?

We deside what direction we want to go, tell the post office to hold the mail and then go. During the week there is always a camp ground close by that is not full. We never make reservations but don't expect to get into a national park when kids are out of school. We have found many places of interest where there wasn't supposed to be anything. Don't make your plans too strict, relax.