Here's some of what I think is my personal best advice:

Learn to live in the gray areas. Don't be dogmatic. The world isn't black and white. Take some parts of the black and white. And, don't be afraid to change your mind about some things.

This may sound obvious to some of you, and sure, in theory this is simple. But in practice? Definitely not, at least in my experience. It requires a change in mindset and worldview, which generally becomes harder as you age ("because your want to conserve the way of life you enjoy").