My secret? It's simple:
1. Unconditional love
2. 100% respect
3. Whenever you feel like arguing, shut your mouth and think again. It will never come out on the same tone and you will find smoother ways to make your point without arguing.
Sometimes, I fail. I let the stress, the outside factors interfere with our life and thoughts. And even if we don't end up arguing (she's very wise about it too) I regret it every time. But points #1 & #2 will always be true.