Achilles tendonitis is a type of overuse injury
which does occur frequently in runners and others who perform physically demanding high impact exercise. It needs to be taken care of, because it can be debilitating chronically and it can also predispose you to a slightly higher risk of Achilles tendon rupture.
Obviously the first step to heal up is to stop running. Continuing to run while you have active tendonitis will only worsen the pain and delay healing. Icing the affected tendon area and taking anti inflammatory medications such as ibuprofen or naprosyn as directed by your doctor
can also be helpful. Another helpful maneuver in the acute period is to use a heel pad to elevate the heal (this weakens the calf muscles biomechanically and takes some strain off the tendon, allowing it to heal).
Once the tendonitis heals up, you may want to consider changing the type of shoes you run in. This is because one of the most common contributors to achilles tendonitis is overpronation. Overpronation can be diagnosed for you by an athletic shoe specialist, who can then recommend a pair of corrective running shoes.
Talk to your doctor if the pain and discomfort from the tendonitis is not improving with rest.