In my experience (almost 40 years), you have to earn to play a repetitive pattern first, and keep at it until the thumb/bass is absolutely rock steady. Then start learning tunes from tablature (or however you're most comfortable learning), where each measure is a pattern, but a *different* pattern from the measures before and after. Keep worrying those strings for a few years, and you might gradually become able to introduce a few variations in the treble/finger part.

I remember -- back before I started trying to actually *do* it -- imagining that I would soon be freely improvising on the upper strings with my fingers while the thumb independently kept a steady rhythm.

It didn't happen the way I had anticipated. For me, anyway, every four-beat figure (whether a repetitive background pattern or an element in a hard-won memorized piece) was a different exercise for the whole right hand. Eventually, the many different combinations of pinches and alternations of thumb and finger(s) each became a riff, and I *very* gradually gained the ability to build different combinations of these riffs in a process aproaching improvisation.

I would also recommend the Stephan Grossman books, and I also dearly love, admire, and recommend John Hurt. In the early 70s I discovered another book of tablature, "Masters of Fingerstyle Guitar" [I think] by Donald [somebody-or-other], which contained several MJH tunes I hadn't ever seen elsewhere in tab form, plus equal numbers of tunes by Mance Lipscomb and one or two other greats. My copy of the book is long-gone, so I can't provide the exact title or the author's last name -- anybody out there familiar with this? In any event, I discoverd this book when I was very active and enthusiastic, playing full-time, and learned a lot from it.

Another issue: attack. For the first 5-6 years, my fingerpicking was overly careful and, in retrospect, too quiet. I made a breakthrough of sorts after a few months of full-time streetsinging, whaling on the guitar with my fingerpicks. At first I would do some fingerpicking tunes (too muted to get much attention out there competing with the noise of traffic), alternating with louder pieces where I'd just strum all six strings, down with the thumbpick and up with the two fingers. Very gradually, and mostly unconsciously, the two different styles of playing kinda melded together and developed a much more emphatic style of fingerpicking, often catching two or three strings at a time with a thumb- or finger-pick rather than carefully aiming every stroke at a single string.

The two-finger (thumb plus one) style is usually more suited to that kind of rough hard approach (e.g., Mississippi Fred McDowell), and in retrospect I wouold proably have gotten there sooner had I not already become a dyed-in-the-wool three-finger picker thanks to Stephan G.

Also: once you develop a little freedom in your attack and become able to play harder, you then have to explore various little tricks like dampening the strings (especially bass strings) with the heel of your picking hand. And, of course, you need to develop enough control to play some parts with delicacy and exactitude and others hard and rough.

Have fun!