My most significant piece of advice came from my uncle. It was simply this "how would you feel if your grandmother died tomorrow?". It had an immediate effect. From that moment on I began to respect and honour my grandmother.
Up until then I was not exactly the nicest grandchild, a lot of anger, a lot of confusion reigned in my childhood and my grandmother was the last in the chain. She ended up getting most of my frustration. But that piece of advice had a lasting impact, it has been with me for about forty years now.
I try to always remember that when dealing with other people not because I think I want to improve their lives, I simply don't wish to have a guilty conscience if they do die tomorrow. Of course the effect is the same as if I were to be motivated by altruist ideals.
For most people reading this it might be a nice ideal but not a good piece of advice. The reason this was a very good piece of advice for me was that a few years before my uncle said this to me, my father had died. He died without me being able to say goodbye, to be able to talk to him, nothing. I was left with a mighty large hole.
And that is the second piece of advice: some advice only works if you have had the experience. And some advice makes sense later after you have had the experience. Be open and listen to others, especially those older than you. Be polite, be reflective and be thankful for being the survivor of a long line of ancestors, not everyone gets to survive.