I've very curious how people figure out what they wanted to do for a living. But I think that the more important and virtual question for me would be, "How can I recognize it when I just did something that made me happy?"
Qualities of happiness for me are subtle, easy, effortless, a sense as natural as breathing. This is opposed to qualities that were more intense, such as no-bad-yucky. I knew right away what I hated, but it was not so easy to learn what I wanted. Things that are not intense require repeated investigation before you really know if you like them or now, or how much it is possible that you might really enjoy them.
So that indicated another question: "How could I check out anything I become interested in doing more of?"
My best strategy that worked really well over and over again was that I would find someone who was doing what it was I thought I might want to do and I'd hang out with them for awhile - being a helpful guest in their life. That would give me a much better sense of what it was really like to do it before I actually did it myself, or trained to do it.
My most brilliant idea to find someone who was doing what I might want to do came from my dad's example. He used to find grown-ups who were doing for a living anything that I expressed an interest in as a child. He was an inventor, so for him my changing whirlwind of interests did not phase him one bit. Because he was 63 when I was born in 1890s, he had seen progress from the time of gas lamps, so he believed that the people who could tell where culture was headed were the creative people.
As I expressed a talent in art, my dad took me to art museums; to art schools; to places where artists rented studios and exhibited in a park together. When I began talking to the DJ, he took me to radio stations. I was horse crazy, so he found a family with a girl my age who raised Arabian horses and paid for riding lessons. He took me backstage at the circus when he saw me trying to do vaulting on a rented horse that I had trained to canter in a tight circle. He dropped me off at the veterinarian's office to help with the dogs and cats that came in. He took me to carrier pigeon exhibitions. He taught me how to get to the San Diego Zoo by myself with a drawing pad and how to dress like the keepers so the birds would sit right next to me.
I'm now thinking of taking his example and doing tours for kids at places where people are working to give them a taste of what it was like to be doing it as a living, as he did for me.
My first dreams were to be an artist, (which included a kind of hippie soiree scene) and to go find somewhere with some people where I belonged that wasn't in an urban area, and then to live as often as possible in a "state of grace" consciousness.
Now it's fun to be ready for new dreams!