Watch the Left-Hand Techniques 1 online guitar lesson by Bruce Arnold from Guitar Physiology Survival Guide

Left hand technique is a complicated matter. Your fingers, palm, wrist, elbow and shoulder must all work together to give you fluid technique. In general they should remain relaxed and should all move in this same way no matter where you are on your instrument. By always moving the same way for any note you streamline the interface between your mind and hands. All joints should operate in the middle of their radii. It may feel strange at first, but give yourself time to get used to these new positions and you will find that you improve rapidly no matter what you are playing.

I recommend using a mirror or taking videos to check that you are actually doing what you need to be doing. I also recommend that you stand up when you practice. In most cases this will be how you are performing and it will prevent a lot of the problems that come from practicing sitting down.