One of the most important things in establishing good technique is learning to relax when you play. Having the muscles tensed up while you play could eventually lead to a breakdown of cartillage or carpal tunnel or arthritis. Not to mention playing w/the hands tensed up will slow you down and cuase your muscles to fatigue out.
Some players will use breathing techniques to help them relax will they play. Are you one of those people who hold there breath will doing a fast or difficult run? Breathing techniques is like doing yoga while playing guitar. It is a known fact steady breathing helps keep the body relaxed and oxygen flowing to the muscles, as well as helps concentration.
Eric Johnson is heavy into meditation. I like to use visual imagery, imagining my hands being lighter then air or my fingers being made of feathers. Practice this technique will playing "air guitar" and then when you pick up your guitar try to keep the same sense of relaxation you had while using visual imagery.