Keep your left hand at rest in its natural curve.

Keep the thumb in a comfortable position around the middle of the back of the neck, usually opposite the 2nd finger, where it can best offset the pressure being applied to the finger board. Do not let the thumb come over the top of the neck unless you intend to use it to play notes or choke (mute) the string. Thumb migration over the top of the neck will force the palm to come into excessive contact with the back of the neck. This shift will reduce your reach on the fret board and will add more contact friction, making position shifts unnecessarily difficult.

Find the most comfortable position for your thumb where it can remain stationary while your fingers move throughout a four fret position. You should be able to execute the five-fret, chromatic scale position across the entire board without the thumb shifting. The thumbs contact with the neck should be on the soft fleshy part ( the center of the thumb print / the ball ). This will require you to bend your thumb back slightly.

Exert as little force on the strings as possible. Make a solid contact between the fret and the string by playing just behind the frets. Most beginning players develop the habit of excessive straining while pressing down the strings. This is due to their soft finger tips and the need to press harder to get a solid tone. Once you have the beginnings of calluses on your finger tips, the string will not press so deeply into the flesh of your fingertips and a solid tone will require far less pressure. You must over come this habit of straining.