The greatest truths are the simplest. I believe the answer to this question is to do more and try more while you're still young.

You have to find/choose your purpose, but never the work. Work should come to you.

Honestly, from what I've observed, you don't. It finds you. Life is funny that way. I think that what people should do is to learn about and try out a lot of different things, to maximize the odds of it finding you.