In no particular order. Staying in love is less about evading dramatic catastrophes and more about avoiding death by a thousand paper cuts.
1) Make sure you are loved back. After a while it gets difficult to respect yourself if your love is unrequited.
2) There are many observations best made only inside one's head, particularly concerning annoying but innocuous habits. Do you want to be constantly evaluated? Didn't think so.
3) Quote your loved one back to him or herself when he or she makes an astute observation. Everyone likes to feel heard.
4) Rib only gently and respect the line. It can move from day to day.
5) Always choose your lover over the cat or dog.
6) When evenly matched, whoever cares more about the subject should win the argument.
7) Joke early and often and especially in times of peril.
8) Let your lover hear you compliment him or her to others. Sometimes we forget to do it to their faces.
9) Protect your lover's pride, always. Always.
10) Understand when a hug is needed, when space is needed, and when sex is needed. Try to oblige.