A few things I have learned after 25 years:
1.) You need to have the mindset that marriage is for a lifetime, i.e. if you have issues, you better work on them and work them out together.
2.) You can't change each other--maybe train, but not change so try to see those annoying habits as endearing or something to laugh about. Work on changing yourself if you need to, but not each other.
3.) Tell each other what you need/want, DO NOT assume your spouse knows. Yes, it would be nice and lovely if they had a clue and could figure it out on their own--they don't and can't so just tell them.
4.) It is okay to go bed angry. Sometimes a good night's sleep is all an issue needs to get resolved.
5.) Support each other, take care of each other, love each other well. Problems arise when we become selfish and only worry about taking care of ourselves.
6.) Pray for your spouse daily.
7.) Find laughter in the little things--life is funny, being married is funny so enjoy the wild ride together!