I try to work on the software I actually use. I don't jump on a random horse and start riding to the West. I think the first step is look at your tools. What problem do you have with your tools. Is the library you using too restricted? Does it have a null/nonetype exception rasied and not properly handle? If you can't solve it because you have no idea where to start, well, at least file a ticket :) I have limited experience too. I think the first real contribution was Ansible, rewriting the hg module was critical for my use. So I did. When I was an intern at Mozilla I learned about CSP so later when I found a few minor issues with the CSP implementation in Firefox I started volunteering. My internship didn't involve a single line of writing Firefox code so it did take a while to navigate through a couple files for a newbie. But grep, mxr.mozilla.org all helped.

I think even just making demos and making documentation changes is equally powerful and useful contribution.