[michaericalribo]

What do you use regularly, that is open source? You'll be more motivated to participate in projects that you use on a regular basis, that might be useful to you.

Find some software that you're interested in. Do you follow their GitHub account, subscribe to the mailing list (especially dev list), keep up to date on changes that are new? Have you looked at their source? Is there anything you wish the software did better, or any bugs you wish were fixed?

Learning how everything fits together for a software project can be a great learning experience, and if you take notes as you go, you'll naturally write docs (and be the hero of the day).