While working through the last two weeks of the Functional Programming course on edX, I took a break to run through the short
How to Use Git and GitHub class on Udacity.
I've been using Git for a while, but this was a nice introduction to GitHub -- the course is very well-designed and felt like a good balance of fundamental principles and practical application.
It also pointed me to these two very useful environment tweaks:
git-completion.bash
git-prompt.sh