I think about this all the time, wishing I knew then what I know now. My best advice is to always listen and keep an open mind in every situation. Think before reacting (count to 10 slowly in your mind if that helps slow a negative reaction). Never judge anyone, always be accepting and put yourself in the shoes of others and think about how you would want to be treated if in the same situation.
As for life in general, seek out adventures and experiences, not "things". Go outside and soak it all in every chance you get. Travel near and far and your eyes will be opened to things you never imagined!; particularly other cultures, climates, and landscapes.