The most common demographic that suffers Achilles tendon injuries are men between the ages of 40 and 55. The most common scenario is that they were playing football (somehow usually on Thanksgiving) and stepped on the ground and felt a sudden weakness in the ankle. Typically these injuries occur in people who are not routinely active and/or do not routinely stretch. So then, the answer to the question is - STRETCH, STRETCH, STRETCH...and also don't overdo it on the sports if you haven't been routinely active.
As we get older, the tendons in the body become less and less able to recover from stretch and are more likely to tear. If you are diligent in stretching before and after any exercise (or even just in the morning and at night to stay loose) this can significantly reduce your risk of experiencing and Achilles tendon rupture. Warming up before strenuous activity is also vital - a light jog to warm up the tendons helps to make them more supple and flexible so they stretch rather than tear.
Finally, if you have pain in your heel cord that persists more than a few days, it is wise to visit your local podiatrist. A quick evaluation can determine if you are in need of some serious stretching at home or if other intervention is needed. Be careful out there!