I believe good communication is the key to a good relationship. If we communicate well with the people in our lives, we are able to better understand what the people around us want, need, expect of us, and what they are able to do and likewise, they will understand what we want, need, etc. This includes not just the people we live with, but our co-workers, doctors, service providers of many kinds...the list is endless.
The qualities should include being able to state your feelings, wants, needs, expectations, etc. honestly and in a clear manner without putting anyone down. When someone has done this, I feel it is then helpful to rephrase what you heard so you know you have understood their meaning clearly. If you have miss-understood something, this gives them a chance to clarify what they actually meant. When people feel they have been understood, they feel like you value them, and that is a nice feeling.