Perhaps I shouldn’t be the one giving you advice when I’m also struggling with my technique, and I don’t want to give you the impression that I know more than what I actually know, but I can tell you about the process I’m going through, small ideas about how to practice that I’ve been trying to follow and small discoveries I’ve been doing along the way.
@Shredd elaborated further on what I’ve tried to say. I believe that if we approach a fast passage like “oh crap, here it comes, I hope I get this time”, we’re doing it wrong. All those guys and gals that can pull off completely crazy stuff don’t look like they are struggling at all. The goal is not to make it through a difficult passage, but to make it feel easy somehow. I often get in the habit of trying to go faster than my ability allows, and I may be able to pull it off, but I feel anxious and tense doing it and more often than not it is sloppy. But what I find is that once I start to get things under my control, it’s like my body begins functioning in auto-pilot. It’s like it tells me “hey, you know what? I’ve got this. Stop worrying so much and let me do my thing”. I think the key is to find a way to let that sensation become the norm in your playing. I don’t think fast passages are much different than any other kind of passage in this regard, your body will be able to get that fast passage with less difficulty once you start developing a sensation of control.
Of course, how you actually do it is the tricky part and it comes with a lot of trial and error. I try to be really mindful of my body. Is there unnecessary tension? Where? How much? When? How do I release it? What is causing it? Sometimes it’s not what you think it is. For example, sometimes I feel tense at one note or passage, because of the following or the previous passage, and I could be misled into thinking that the passage where I feel tense is what’s really causing me trouble. Let’s take whatever passage is causing you trouble. Is it the right hand, or the left hand? Or both? You can try, for example, developing your left hand first, so you can focus on the right hand later on. You can slow down, play it really slow and without a metronome (so no need to play at tempo, in fact I would advise against it. I would use the metronome more as a test of your ability, so I would practice the passage first no-tempo, and only later on using the metronome to see if it’s working). Take the right hand now, for example. What happens if you try to play it at tempo? The tricky thing is that the technique we use to play fast might not be the same we use when we play slow, so we might need to experiment a bit with it, we can try to find a fast motion that might not be entirely accurate at first, and then slow it down to work on that accuracy and bring the speed up again later. Does it work? If no, why?
I would say it is a very experimental process, and it is also a very physical process and it helps to have a good awareness of your body and the smallest physical sensations that you might feel. I think it’s a good idea to do some body scanning type meditation exercises, as it might help you become more sensitive to your body. For the very same reason it’s a good idea to have a comfortable, healthy posture, not only playing guitar but other times as well. If you don’t, if you’re routinely telling your body to ignore any discomfort, pain or restlessness it might feel, who’s to say you’re not doing the same when you play guitar? It’s all interconnected, good awareness of your body outside the practice room will lead you to better awareness of your body when playing guitar. Unfortunately, there are a million ways we ignore our bodies in our day-to-day life, from the very first day we go to school and have to sit down for hours and hours, to when we work day jobs and also have to sit still for hours or stand up for hours, stay up even if we feel tired, etc. I think playing guitar, or any instrument for that matter, is a call to get back in touch with your instincts, learn to listen to your body again and try to overcome decades of social conditioning. Perhaps that’s why it can be so difficult