So many great advices here 😊
What I learned from my love relationships is: use your downs and mistakes to examine your personality, your behaviour. Is there some side of yourself that could be smoothed out to become a better person? And you must develop this procedure firstly for yourself, and this will automatically reflects in your relationship.

Another important thing is trust and honesty. Express your deepest feelings to your partner and educate yourself as a couple to do it frequently. Knowing each other so deeply is essential to avoid misunderstanding that often leads to fights and breaks.