I've always started with some clear idea of what the right way was – the right way to grip the pick, the right way to position my wrist, the right angle for the pick to cross the strings. (These “right” ideas were different each time I took up this challenge, by the way.) Regardless of which element I focused on, I always ended up with a sore wrist and no progress, and went back to using my fingers instead.
Then, about a year ago, I started playing regularly with a group of friends. There are usually five to ten of us. The songs we play are mostly swing-ish tunes from the 1930s or country songs from the 1950s. The repertoire works best with a pick, and it's fairly straightforward. If I play the right chords, keep the beat and don't drop the pick, I'm doing the job. This is fine until I switch from playing chords to playing a melody; then it's a train wreck. This has brought pick technique back to my practice schedule.
Again, I started with clear ideas about grip, pick direction, wrist position, pick angle, and the like. That approach still sounds good, but since it has never actually worked for me, I'm coming at it from the reverse angle this time.
Now my goal is not to move the pick a certain way. My goal is to get a clean, clear sound with relaxed, pain-free hands. I'll practice with that goal until I get there; then I will look and see what my hands have decided is the right way to do it.
This changes a lot. Before, I was relying mostly on my eyes for information. Now I pay more attention to how my hands feel and how the notes sound. My posture is better, because I'm not looking down at my picking hand. I can practice longer, because my focus on having relaxed hands keeps tension from building up in my wrists, arms and shoulders. Focusing on relaxation also keeps me thinking about playing smoothly, rather than playing fast. (“Fast is not the target. Smooth is the target. Fast is the bullet hole we make when we hit the target.” - from First, Learn to Practice)
I enjoy this process more as well, for all those reasons plus another. This way of working is creative; I'm creating a technique by trying things and keeping what works. The things I try are hard to describe in words, but I can tell how they feel and that's enough. It's a very satisfying way to work.
The old way didn't feel creative at all; it was an effort to conform to an idea, to fit into a box. Even if the box was right (and I'm not sure it was), trying to fit into it felt – well, like trying to fit into a box. There may be some satisfaction at the end, when you're in the box, but you can't prove it by me.
Finally, I think this approach is truer to experience. Practicing is about motion; we're searching for and mastering the ideal motions necessary to create music. It is always going to be the body that determines the most effective technique. The head can offer suggestions and encouragement, but it's the body that has to actually do the work.
So for now, at least, the hands are teaching the head.