A few years back I bet my mom I could beat her int he Georgetown-Idaho Springs half marathon. I lost h:

I'd get shoes fitted at a store that can analyze your gate. If there's anything weird about your form, you can seriously fack up your joints. Other than that, I just took it easy and only increase distance in small increments. I'd also work in a hill run once a week. Doing other physical activities (weights, biking, swimming, etc) will also help keep your body going on days off from running.

These days I only run twice a week about 4 miles (8 total).