The more rural or residential an area the less chance there will be for anyone to notice you are there and it will be quieter during the night. The last place I would stay is in an industrial area or in a public parking lot where delivery trucks are likely to arrive in the middle of the night.
A big advantage for us as been the compact size of our rig as we can park it almost anywhere and be out of the way and out of sight.
In many towns there are places you would not think of where it is OK to stay overnight including town parks or water treatment plants and it is worth phoning the local police department and asking. They know where it is going to be safe or not safe.
We always have a planned destination for the night and a backup or two should we decide to shorten the day's drive or make a detour. Google Maps and search nearby works great to find places and using the satellite view we can determine ahead what the surrounding area is going to be like long before we arrive.