I have seen too many times young or inexperienced guitarists having to go back to basics because of poor left hand posture. In this video I'll give you some tips on how to better your left hand posture following a few simple concepts:

1. keep your knuckles parallel to the fret board

2. Keep your thumb opposite your fingers on the other side of the neck

3. reach out for frets bending each individual finger

4. 'scroll' down the neck in a relaxed way like it was a rail, in a relaxed way

I think the most important thing is that you have to be very relaxed in doing all of the above.