Charl Botha has posted an excellent video on advanced rebasing with Magit. It serves as a great followup to Howard Abrams' Magit tutorial video. Abrams covered rebasing too but Botha shows how to perform more complicated tasks.
First he shows how to change the commit message for any commit not just the last one. Then he shows how to easily reorder and combine (squash) commits. Squashing commits, especially, is a common task and a useful thing to be able to do. Magit makes this easy but it's not obvious how to do it so having a tutorial is nice.
Finally, Botha shows how to break apart a commit into two or more separate commits. As he says, this is rarely needed but is possible and not too hard. Watch the video to see the details.
If you haven't already watched Abrams' video, watch that first and then take a look at Botha's video. I learned a lot from them and if you're not already comfortable with rebasing, you will too. Definitely recommended.