DO: Communicate at all times about everything.
This one is so obvious. And yet, so many people fail to follow it! If you're going to be in a long-term relationship, you need to be able to share everything with your partner. You also need to be able to talk through your problems and work them out in a civilized manner. You even need to be able to talk about the way that you talk to one another so that you know which forms of communication are most effective for each of you! A good relationship is all about good communication. Don't ever forget it.