communication coupled with a willingness to listen
If you communicate your sexual wants and desires to one another, you can procure a mutually satisfying sexual aspect to the relationship, or discover that you aren't fit for eachother if a strong sexual connection is important to one or both of you.
When you communicate openly your desires for the future status of the relationship, you can help avoid messy breakups due to different goals.
Communicating general thoughts and feelings on a day-to-day basis with your partner or prospective partner, you get to know one another and basically how the other person ticks. Being careful to pick only important battles to discuss/argue is a sign of a mature communicator who cares about the future of the relationship.