I found Giles Bowkett's for-sale video, which covered contributing to open source along with many other things, helpful. Contributing to the open source community way easier than it sounds. Contributing to open source code, specifically, in a noticeable way, is probably harder, but not that much harder.

http://gilesbowkett.blogspot.com/2010/03/programmers-what-to...

It didn't even take a week after I watched it for me to start implementing his suggestions.