One of the best things I ever did was take a 3 day beginner machine quilting workshop with Cindy Needham.
http://www.cindyneedham.com/workshops.htm about 4 years ago. I had never done any FMQ at all. I knew I wanted to learn how to do it and this workshop seemed to fit the bill. Cindy is an awesome teacher. When I left my cord at home on my (unsuitable anyway) sewing machine she lent me hers. I was the least experienced person in the class.
The best part about having her there was she teaches you to how to solve tension and other issues on your machine. I ended up buying a used machine from one of the other participants the second day, similar to Cindy's. I sat next to someone who had just purchased a similar machine so in addition to Cindy's help we helped each other. By the time I got home I knew how to adjust upper tension, lower tension without any fear. When I have a tension problem I run through her steps and am able to trouble shoot my problem. and of course I found the hum-purr someone else on this thread talked about.
I got a new machine last year, took a one hour lesson in the store and because of Cindy's class could immediately start FMQ on the machine. I think the biggest frustration with FMQ are the machine issues and tension problems and she helps you solve these.
We tried numerous kinds of Superior threads so learned how to adjust tensions on different threads cotton poly metallic etc. I learned many different basic FMQ designs. We even played around with stencils. She covered everything and gave us all a CD with all the information in book form. I still refer to it. While her work is exquisite she shows everyone little tricks to make the FMQ easier and the ways to 'hide' mistakes. I went out of there with such confidence. We learned putting the quilt sandwich together too.
I don't usually take workshops, too hard to get there and expensive. Since then I've taken a lot of Craftsy classes with Angela Waters and Leah Day. I use Leah Day's website extensively and purchased a few of her e-books.
I quilt very differently than Cindy, she does whole quilts and uses stencils extensively I tend to Angela Walters style with free form FMQ but Cindy's workshop was really a great workshop to jumpstart my fmq and skip past most of the beginner challenges.