This post on Blog Pseudoaccidentale described, by way of a parable, how many people think, incorrectly, they can’t contribute to open source. (The article says “FreeBSD”, but the rule applies to any open source project) It’s a matter of doing something, no matter how small, consistently.
I’d even use that analogy differently and say, “How do you eat an elephant?” Hint: see title.
(Thanks, Matthias Schmidt, for the link)
You are right, of course, that the same applies to any open source or free software project. I just wrote about FreeBSD because that’s what I am more familiar with, and that’s the project whose “contributor howto” links I had already posted in a related email thread :-)