Tight calf muscles are a major contributing factor to heel pain. Therefore it is really important to keep your calf muscles flexible and long. This will greatly reduce the tension in the plantar fascia, thereby preventing the occurrence of Plantar Fasciitis and helping to heal any damaged, inflamed tissue in the fascia.
Stand up and place your hands against a wall at about eye level, or put a chair in front of you and place two hands on the top of the back of the chair. Extend one leg about a step behind your other leg, so that one leg is straight and the other one bent. Keep the heel of the straight leg on the floor and lean forward. You should feel a strong pull in the calves. Hold this position for about 20 seconds and repeat 4 times.
You can do this exercise during day, say 2 or 3 times a day and importantly before any sports, running or walking. To make this stretch even stronger during the stretch lift up the arch of the foot, by rolling the ankle slightly outwards.