Keep a balance between separate and united lives
The most successful couples say that, even when all they want to do is hole up for the weekend, they force themselves out of bed to go see their friends, or go meet up with their softball league or go do something that they do separately, as individuals. The flip side of that is that couples that lead very busy lives make a point of conjoining their lives whenever they can. One person sacrifices their event to accompany their partner to theirs. Maintaining a feeling of sharing your lives, while still having your own identities is paramount to fully enjoying a relationship.