Never forget or lose sight of the good qualities that led you to marry your spouse in the first place. Keep noticing all the good things.

And don't forget to tell your spouse you've noticed the good things they do or the traits they have that you particularly like. (It can be all too easy to complain about the things that annoy you - so it's crucial to balance that out by praising/thanking for the things that make you happy.)

Fight fair.
Take turns.
Be considerate and mutually respectful.
Be honest, in the kindest possible fashion.
You have great power over each other's decisions and actions - and you must take great care in how you use that power. Don't use it any more than necessary.

You can make each other very happy, or very unhappy. So you just have to keep making the choice to be a good friend and supportive partner to your spouse.