By saying 'successful marriage', I think you mean successful in relationship as husband and wife. If it is so, the first and the foremost, for any relationship to be successful and long enduring, understanding each other is very important and this is more so in the case of marriage, where a relationship is formed for a life.
When I say, 'understanding each other', it means a lot. We are all unique in our own way. Every one of us have our own likes and dislikes as well as needs and wants. Therefore, in a marriage, both husband and wife should learn to respect each other's views, likes etc. This basic understanding between husband and wife will only help you to lead a successful life.