Specifically check out this presentation here http://gitcasts.com/posts/railsconf-git-talk
The pdf of that presentation is also available there. Understanding the concepts of how git works internally is very easy and helps a lot in understanding git commands and improves your mileage with git.
For users on Windows, tortoisegit is has come up quite well. It's almost feature-equivalent to tortoisesvn and has 25 more features relevant to git.