A month or two ago I was on the #rust IRC when someone discovered that
pow() didn't act quite right for unsigned numbers.
This was a bug that was isolated to a single function, so it seemed like something that I could handle.
The issue got posted, I claimed it and debugged it, and actually managed to fix it!
It took a little while, but very early this morning PR #34942 Fix overflow checking in unsigned pow() was merged.
Now I'm a contributor to Rust!
Try to find a small thing that you can fix in something that you use. Somewhere in there is the right issue that you can fix. It's a great experience. (I really look forward to the release notes for 1.12...)
Update: It turns out my fix made it into the 1.13 release, and my name is in the contributors section in the release notes.