If you had to give one piece of advice that is pretty much universally applicable, what would it be?
I wouldn't dare defile Douglas Adam's memory by not mentioning that you should keep a towel with you at all times, but my second contender is a surprisingly short three-parter:
It's the basic driver of all somewhat intelligent life on earth.
Do something - fail - explore alternatives - do it again - success? Keep it. Fail? Back to exploring and retrying.
Whether it's babies learning to walk or you overcoming difficult situations in life. We should embrace errors and failures of others, as it's an opportunity for them and us to learn and prevent similar mistakes in the future.