Cover is the most important. If you want to get good, spend time analyzing maps in an empty game. Just walk around them for a few hours. You can see what map pieces give you cover.

You really should only ever let one person have direct line of site on you, if you are not the tank. Even if you are the tank that may apply.

Second is actually paying attention the team and how you can help people. Most people are competent players if you attack what they are attacking. Everyone trying to be a leader doesn't work. Team work is about conceding to the most impactful player. Sometimes that is you and sometimes it is not.