I’ll be brief: the best introduction to WiX I’ve found on YouTube. The video by AngelSix is available at this link: https://www.youtube.com/watch?v=6Yf-eDsRrnM. It lasts over 2 hours, but it is worth it - I have not been able to find an introduction as good in written form.

In addition, a small collection of tips and tricks from the SO: https://stackoverflow.com/questions/471424/wix-tricks-and-tips.