I used Harriet Hargrave's book on machine quilting to teach myself. Made up half a dozen practice sandwiches for starters. Got decent with FMQ that way, *but* I hated moving quilts around to do it. Never got over that, even for baby quilts.
I finally purchased a used Voyager 17 and Hinterberg frame (a relatively inexpensive way to start frame quilting, moving the machine instead of the quilt) and love it! For me, it is so much easier than trying to move the quilt around. I just quilted a queen-sized quilt for my sister in a week and it was *fun*! Just the month before I got the frame, it took me a week to FMQ a crib-sized quilt on my DSM and it was drudgery and tension (no pun intended) the whole way.
I'm thinking some people are suited to one approach, and some to the other. I'm definitely one who prefers to move the machine!