They communicate effectively.

It’s been said many times before, but it’s true: great communication is the cornerstone of a great relationship. If you have resentment, you must talk it out rather than let the resentment grow. If you are jealous, you must communicate in an open and honest manner to address your insecurities. If you have expectations of your partner, you must communicate them. If there are any problems whatsoever, you must communicate them and work them out. And communicate more than just problems – communicate the good things too.