The illustration above shows good left hand position. It is important
that your wrist be close to straight. This will enable the tendons
in your hand and wrist to move fully and with strength. If you bend
your wrist too much it can, over time, cause physical damage to
the tendons. (carpal tunnel syndrome)
The illustration at right shows the wrist bent too much.->
Another common bad habit that beginners pick up is the
positioning of the thumb. Too often the thumb is wrapped up onto the
fingerboard of the guitar. This is shown below.
You should keep the thumb in the back of the neck and usually not
bring it any higher than the fourth or fifth string. This will enable
your fingers to do their work properly. It will also give you the
ability to reach a larger span over the fingerboard with increased
speed.
The illustration at the right shows correct positioning of the
thumb.
A Note about the positioning of the Left hand:
This is just a recommendation and guideline. Different people do play
differently and you should always be comfortable when you play. Do
not sacrifice enjoyment of playing in an attempt to achieve perfect
form.