With 50 yrs. of marriage, my biggest lesson was to never say anything I'd regret later. We were never the screamiing throwing things kind of people. We just stayed silent til one of us got lonely & broke the silence. LOL. Then we'd talk about why one of us was unhappy.
Not always a good thing though since one of our sons once told me he didn't learn how to resolve conflict since he never heard or saw us argue. Good point but that's just how we were.
The obvious first in line priority is just to always remember that you love ea. other.