It's hard to just "pick a project" and start contributing. You need a little bit of passion, excitement, or just plain need. Look at the tools that you already use and depend on and start there.

Odds are you know how to set them up, configure a few things, and the like. In most cases, a few pull requests to the docs are not just welcome but greatly appreciated.

(I've been managing projects since 2007 and participating since 2001.)