Exercise, though others have said that. Personally, I'd say that the thing that changed my life for the best has been Not Giving Tech Support. When I was a teenager I was kinda miserable because some people abused me for tech support. You know, it's nice to give favors, but at some point you're fed up of reinstalling every computer in your block every 6 months. People stop you on the streets and the first thing they…
I am still in college (not so old) and I can relate to this. A new variation is "I/My friend have this awesome app idea and we need a IT guy to code it out. Can you help?"
Lesson learned: just because you're family (or friends) won't mean they're going to uphold their end. Let them work for it first.