Tight calf muscles contribute to shin splints. A good exercise for stretching these is to stand on a step with the back of your right foot hanging over the step, and the left foot entirely on the step. Slowly let the right heel drop until you feel your calf muscle stretch. Hold for about 30 seconds. Repeat three or four times. Then change feet. Also, you can try this stretching exercise with your knees slightly bent.
Another exercise is to stand near a wall or chair (for balance) and slowly raise your toes and balls of your feet as far off the floor as you can. Hold if for three seconds. Work up to three sets of 10 lifts, three to four times a week. This will help prevent shin splints. Also, keep doing your PF stretches. A deep massage in the aching area can also help.
This info comes from 'Prevention' magazine. In my experience, stretching is one of the least pleasant things to do, but probably one of the most important. Hope this info will help you.