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 say is "you know I think my computer has a virus...". Yeah, f* you.
I guess not many people in HN do this anymore, probably because we're kinda old, however, if that's your case, learn to say no. It's fine. You can still oblige for some people. However, never do it for free. With close family and some friends, they probably have had more deferences towards you than you can ever repay. For others, just say "I do this for a living, it'll be $XX, at friend's price"
Once I started charging, only a few people took me up on it, and they've always been happy with the result. Those who want tech support for free should give something in return besides a beer "for your inconveniences".
I could expand but I'm afraid it would be an ugly rant. If anybody wants any help on how to say NO, just ask :)