People do sometimes get complacent, but in most successful marriages, the couple maintains a dating mindset. They do not take the other for granted. They make special efforts to look good for the other person. The surprise trips and sweet notes common before they got married continue to some degree. The couple also prioritizes sexual intimacy and creativity in bed. Spice keeps a marriage healthy.
Both parties in a marriage should be individuals in their own right. For example, they should have some separate hobbies and friends, providing it is without conflicts. They can share many common interests, of course, but they are not co-dependent, nor do they stifle each other. A certain degree of time apart allows couples to come together and bond over their separate experiences and adventures.
Spouses should talk to each other whether the marriage is doing great or when it is going through rocky times. Marriage is not the place to let jealousies or resentments fester. Many couples even choose therapy for calm times but especially for troubled times when communication becomes difficult. They prioritize being able to communicate to their partner and view talking to divorce lawyers as an absolute last resort.