As you learn and become better you need to begin to thing about how to set up for the next chord. If you form a G chord with your middle, ring and pinky fingers you fingers will almost fall into a C chord without effort. Learn where your anchor points are and use them. With a lotta chords your middle finger (or ring finger) doesn't have to move in order to form the next chord in the progression. Think of the key of G. Form the G chord with the middle finger 2nd fret 5th string, ring finger 3rd fret 6th string and pinky finger 3rd fret 1st string. Without lifting up the middle finger you can "roll" right into the C chord. You can discover many chords where the same principle can be applied. Look at the chord fingerings for the various progressions and you will start to see what I saying. Also, and this is important - as you are changing from chord to chord NEVER EVER stop strumming. I would rather have a strum of all open strings than lose timing of the song. As you learn start off slow and build up speed as your ability and timing allows.
Nela