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
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.