Put stickers on the map for things you want to see.
Decide which stickers are close to a reasonable route.
Decide which exceptions and detours must be made.
Discuss planning ahead versus winging it.
Discuss making reservations versus showing up and hunting for a place to stay.
Discuss short drives with time for sightseeing, or 8 hour drives with time for dinner, versus 15 hour drives where you get in at midnight and still have to make camp.
Note: the person who does the planning gets the last word.