Once again, another great article I pulled off the web.  Please read before doing any running.

How To Avoid Injuries . . . and stay out of the doctor's office

The majority of running injuries occur from overtraining. Avoid doing too much too soon. Your progress in mileage and speed should be a gradual one. An unrelenting increase in mileage from one week to the next will ultimately result in a break down. It is important to keep in mind the principle of hard days and easy days being interspersed and also hard and easy weeks. Mileage should usually only be increased approximately 10 per cent per week. Every third week, you should drop back a small amount. For most runners one or two days a week, at least, should be devoted to rest or non-running activities. This gives your body a chance to recover and strengthen itself. It is helpful to maintain a running diary. This should contain your mileage, course and brief note on how you felt. It may help trace the origin of problems related to overtraining.

You should always ease into speed work. One way to ease into speed work would be by throwing in a few short distance surges into your normal runs. Gentle hill work, prior to speed work has also been recommended by some coaches. Track workouts should occur after you have accomplished some faster paced running during the course of your routine runs and should not be overly ambitious at first.

Running shoes should regularly be replaced. Shock absorbing capability will diminish gradually and may be inadequate after 350 to 550 miles. The upper of the shoe may not show much wear, but the shock absorption may still be gone. If you are running 20 miles per week, you should be replacing your shoes between 4 and 8 months depending upon your shock absorption needs. It is always cheaper to replace your shoes than to make a visit to the doctors office.