This reminds me ... I've run across an online Mastering course that looks good to me. This guy Rob, who can't be more than 30, has a nice teaching style and has made some instructional videos that are produced at a highly professional level. There's a free "mini-course" offered within this infomercial:
https://www.youtube.com/watch?v=k0FpX200S1s Hope this helps somebody interested in improving their skills. Note: I have no affiliation with Rob. My daughter would like him to be my son-in-law, though.
Cheers,
Eddie