This is particularly more difficult if a relationship is still young. The truth about people is that messages are always encrypted. This means you have to know what your partner's patterns are to be able to respond how they want you to. Try to be conscious about what the other is expressing all the time. Not being able to respond according to how one wants you to means that you do not know your partner and you should know better. If you do not know how to respond, it is better to keep everything neutral as the person usually leads you to the appropriate response. You have to keep on guessing.
People are naturally egocentric and that becomes a problem when it comes to relationships. Most people are biased with their own interests that the other ends up neglected. Most of the time, people put the blame on others and forget their own mistakes. People who want to have a healthy relationship should always consider what the other person has to say. This means that if you want your relationship to work, you have to put yourself in the other's shoes once in awhile. It would be easier to compromise in that sense.
In connection with the usually egocentric nature of everyone, people tend to think that having a relationship means that lives of a couple should revolve around each other. The truth is that kind of a relationship is too dreamy. It only happens on movies and it is quite impractical to think that another person can actually "complete" another. The elements of a relationship are so complicated that it is almost difficult to put them into words.
Although a relationship has to be mutual, a healthy relationship is not absolute. This means that each should still be allowed to have lives of their own instead of doing and facing everything together. For example, each should still have time for their respective friends and families. Contrary to what usually happens, it is alright even if you do not do all of these things together. Even other interests and leisure do not have to be done as a couple. Spending time with other people does not mean you love your partner less.
Spending things you enjoy by yourself or with other people make you a perfectly independent individual. What makes it even more ideal is that you would not have to worry about your partner not enjoying her time. People who want to have healthy relationships should keep in mind that it should not always be about spending quality time with your partner but also about spending quality time with yourself. Having some breathing space would make both of you better individuals and it would definitely lead to being "complete".