THE LEFT HAND:
In general, with your left hand, try to follow the rule of "one finger, one fret". Your four fingers will allow you to cover four frets without having to change the position of your hand on the neck. Be sure you press down on the string just behind the fret, not directly on top of it. Also, try to pull with your shoulder and back muscles when fretting notes. The thumb exerts a little pressure but is mostly a guide.