The best is to find a project for software you like and use. You could
start by testing, fixing bugs, sending small patches (including the
doc), etc. Keep tracking on the news and development.
Start little but do start something. I'd say the size of the project is
not much an issue. There are always things new comers can do. Request
the maintainers if you can't find anything. If you like the project,
you'll be more and more understanding what's going on and how it works.
At the beginning, you'll feel the efforts quite big for little results.
Do contribute again and again. By being active you'll become more and
more comfortable. Someday, you'll become a influent contributor.
Here is the big secret, really.
--
Nicolas Sebrecht