Suction cup mounts for smartphones and GPS units are popular choices among many, but they aren't legal everywhere in the United States. In other states, they may be legal, but must be positioned and used in specific ways.
As a truck owner, I always drive with my tailgate up. However, I've known people who would drive with it down claiming it gave them better gas mileage. I'm not sure if that's true, but I now know that it's against the law.
With technology changing in vehicles today, some of the training that you got when you were in high school might be wrong or cause injury. How you hold your hands on the steering wheel will make a huge difference.