There are many ways to do it; you could follow chromatic's advice and run and write tests. You could answer questions usefully. You could identify a problem or something that's missing, and fix it (that's how many, many good modules got on CPAN). Do it in a way that is useful to others, not just yourself. But don't get carried away in generality. The trick is finding something you (personally) find rewarding, so you stay motivated. Keep asking yourself if you like doing it, and if you find that you no longer do, switch to something else.