The number 1 rule I was taught:

Do not disrupt the flow of traffic.

Don’t park in the passing lane doing 50mph, don’t stomp on your brakes to make a missed turn, or dive across 3 lanes to make an exit. If you screw up, don’t make every other driver around have to deal with *your* problem.

This covers so many driving sins that it should be the first thing taught to new drivers. Frankly, combined with “situational awareness is your friend”, that covers almost all on the major problems I see.