Keep your body and mind guessing. Clock a variety of routes so that you're not running the same one every day. Choose different distances and terrains. Consider a 5-mile run in the neighborhood one day and a 3-mile trail run another. Vary your pace by alternating shorter, faster runs with longer, slower runs.
Change it up with cross training. Cross training uses different muscular groups and pushes your body in new ways. Yoga for running classes can stretch out the body, preventing injury on sore muscles. Swimming or fitness classes can give your exercise regimen a good balance. Choose cross training activities that work on a wide range of muscles while continually increasing your cardiovascular health [source: Marathon Training].