I have to add wix-users@lists.wixtoolset.org. That's where everyone hangs out and asks/answers questions as they come up. Just lurking on that mailing list will provide lots of real-time education on the WiX toolset.
One of the best ways I found to learn WiX was to take an existing MSI that did something I wanted to do, and used the Dark decompiler to generate a WiX script from it, and then I read that.
Chiming in with another shameless plug; I recently wrote an article where I somewhat desperately try to explain some of the concepts of WiX in a more easily-understood way than the others. No offence.
It is meant to be read before reading any tutorials, because it specifically tries to address some of the things people always seem to misunderstand as a result of well, reading those tutorials. And especially the documentation. At least I did.
Also, there is another article, a little bit more advanced, that has an angle to those distributing script(like Python etc)-based systems, and why one in not only those, but all cases should use Paraffin rather than Heat.
