The following is a very basic exercise to develop security, independence, and most importantly, efficiency of muscle movement in your fretting hand on the guitar.
In the case of this exercise, you should focus on relaxing all of the fingers, as well as the arm and shoulder.
The underlying movements of this exercise consist of putting finger after finger on the same string, starting with the first and ending with the fourth and then reversing the direction. The result is a 4-note chromatic scale going up and down.
While doing this exercise, you should actively relax any and all muscles that are not needed to produce the desired note. The idea is similar to the relaxation technique known as autogenic training. The fretting finger itself should be thought of more as a relaxed curve than as a clamp that, in conjunction with the thumb, “presses” down on the string, or squeezes the neck of the guitar. Thinking of your fingers as relaxed curves also encourages the weight of the relaxed arm to assume the responsibility of depressing the string. The rate at which you move from note to note is determined solely by the onset of relaxation. As you get more used to this exercise, your muscles will learn to relax at ever increasing speeds, until relaxation is practically instantaneous.