I cannot agree with Guitarpicker and the rest of this panel more. I begin every class with my students by playing a simple exercise. Put your thumb on the sixth string, and all four fingers on the first string. Simply play (free style) thumb, one two, three, four three, two, one thumb - back and forth until it becomes as natural as breathing. The second exercise is to place your first finger of your left hand on the first fret of the first string (it will not sound particularly good) and play the same right hand exercise. After your have completed at least two repetitions with the first finger, add the second finger while holding the first finger down, then the third while holding the first two fingers down and finally the fourth. Then, take away one finger every two repetitions until you are playing the open E string again. The third exercise is to play the same pattern, but put down the first finger of each hand together, then the second, then the third, then the fourth. This time, instead of changing fingers, change positions! The first two repetitions should be in first positions, the second two in second position and so on. Start by doing at least three positions and as your strength builds up, add positions. When you feel comfortable, do just one repetition in each position from first to tenth position. By the time you get to this point, the fourth finger should feel more or less natural.
There is a physiological reason for doing this as well. If you exercise the fingers in your hand unequally, the overall health of your entire arm may suffer. If you exercise the first three fingers, you really should include the fourth one! My fourth finger was injured in a rafting accident when I was a child and most of the mobility (not full mind you, but vastly improved) I can credit to my time with my instruments. Since you already use your fourth finger on your fingering hand, I think you will quickly thank yourself for including your fourth finger on your other hand as well. By the way, if you are left handed, simply reverse the instructions. My left dominant students all do.