I found a way to analyze my picking technique, and it's helping me clean up and stay clean. I made categories for all picking mistakes. This makes them easy to spot. The idea is that if any note is not picked perfectly, then it should fall into one of these categories. Note that this concerns only the picking hand.
- big whiffer (totally miss the string)
- pick too early
- pick too late
- unwanted pick contact
- with another string before note
- with another string after note
- with same string before note is done
- unwanted finger or thumb contact
- with any string before note
- with any string after note
I just keep this list in the back of my mind whenever I'm trying to pick cleanly. I don't need to watch or listen; they can all be felt pretty clearly if you're paying attention. If I'm doing meticulous slow-tempo practice for perfection, I'll stop and bring the tempo down whenever a mistake pops up. Otherwise, I just try to never let them go unnoticed, making a mental note whenever I feel one.
There are always other dynamic considerations. Maybe you didn't hit a note hard enough or didn't palm mute it the right way. These are also important, but there's no clear right or wrong, so they're more complicated. You also really need to listen for that kind of playing, you can't just feel it. Perhaps I will write about it later...