I've been doing a lot of overhauling of my technique lately (a scary thing to do after 14 years of playing). I had been focused mainly on the right-hand, but after seeing Ben Monder last month I've been thinking a lot about how to get my left hand to play more effortlessly (not surprising after one sees Monder!). I had always thought I had good left hand technique with the thumb well behind the neck like all my teachers told me, but there was too much tension in my left hand because this led to me constantly "pinching" the guitar, and for the past few years my hand got very weak after only a few hours of playing.
So here are a few things I've done that have helped:
1. Shifted my position so the tip of the thumb is visible from behind the neck.
2. Played with a piece of tape around my 4 fretting fingers, above the knuckle and just below the first bend in the fingers. It's totally weird feeling and not exactly how one would play for real, but it's taught me how keep my fingers closer to the fretboard, and to get around the neck without pivoting off my thumb.
3. Trying to get the fingers to work independently, meaning the force that applies pressure to the string comes from that finger alone, and not from leaning or pivoting off another finger.
So anyways, I'd like to hear what other people have learned about this subject, or if someone can point out some good books/videos that hit on this topic that would be great too. I'd especially like to hear if someone has heard Ben Monder talk about how he developed his left hand technique!