As far as I know, there's only one book on the subject. MC is hard to learn just by reading the book. When I learned MC, I went to a large "coding center" and coded ecgs with a experienced supervisor who gave me feedback.
I would say that coding has a limited use in clinical practice since its main purpose is to quantify changes for epidemiological studies. With that said, after learning MC I got a more detailed knowledge about ecgs which reflects into my every day clinical work.