This is going to sound kind of lame and abstract, but make people happy. Obviously it can't be everyone, there are other really important things in life, and I've learned some people aren't even all that interested in being happy, but basically what it says.
When I was a kid my family played a lot of board games, and we had one called "Careers." At the start of the game each player had to secretly assign 60 points between fame, fortune, and happiness, and the winner was the first one to gather enough points of each type. The simplest strategy was to just go for 20 points of each, but even as a kid I always weighted it 25 happiness, 20 fortune, 15 fame (I'd have gone heavier on happiness than that, but going too unbalanced was bad strategy). Happiness was always the priority with me. I think that was one of the reasons that I've preferred working at small companies, one person can have more influence on the corporate culture to make it a happy place to work.
I wouldn't say no to somehow managing to write a fantasy or science fiction novel that some people really enjoyed, but I sometimes wonder if I might not have enjoyed working towards becoming something like an editor, helping people's writing really shine so that they could be succesful? It feels like that would be an amazing feeling, knowing you helped someone reach their goals and helped them make a bunch of other people happy?