Put this in your bashrc:

    source /usr/share/bash-completion/completions/git

And you can type "git br<tab>" to write "git branch", "git checkout fun<tab>" to write "git checkout funky-feature", "git log --na<tab>" to write "git log --name-only" etc.

Pretty much every time you press <tab> somewhere while writing a git command, it does the right type of completion. And hitting <tab> multiple times lets you toggle through the options. So you learn git along the way.

This was one of my most enjoyable productivity jumps when it comes to using git.