Where common notes occur between chords (e.g. 2nd finger in C chord and A chord – as in the following example), keep the finger down when changing. This is called a pivot finger. It will result in a smoother sound.
Another important aspect of left hand technique is the use of guide fingers. This involves keeping your finger on a string and sliding it to a new position on that string when changing chords. E.g. when changing from a D chord to an A chord, keep your 3rd finger on the 2nd string and slide it back from the 3rd fret to the 2nd fret. Like the pivot finger technique, the use of guide fingers helps to create smoother sounding chord changes. The following example makes use of guide fingers between all three chords.
This example uses both pivot and guide fingers and contains all the shapes you have learnt.