Read, read, read. There's so much valuable information on the internet. I took an online course, but frankly, it really wasn't nearly as good as just reading blogs, web sites and, of course, the QB. Buy a few old machines of various ages and makes. Maybe just start with Singers, since they are so simple and straight forward. Here's a few web sites to get you started:
http://www.tfsr.org/publications/tec...achine_manual/
http://www.ismacs.net/
http://mysewingmachineaddiction.blogspot.com/
http://www.treadleon.net/
http://vssmb.blogspot.com
Now...the hard part will be how to STOP buying old sewing machines, but that's a different topic.
~ Cindy