Running a race not only helps to motivate you to improve your personal best, but always a great way to stay in shape. The months of training involved are critical. It's important to run the suggested amount of mileage each week. Running significantly under mileage or over mileage can hurt your time and hard work. Working significantly under or over the suggested recommendation can damper your performance because either you will be working your muscles too hard or not enough.
Find a race. Join or create your own training group. Run the recommended amount of mileage with a few tweaks to fit your running style. Eat healthy with proper nutrition. Most importantly hydrate your muscle. Without correct hydration your muscles won't function properly. Keep yourself motivated with a race or challenge. That way you have some competition to look forward too while staying in shape.
After crossing the finish line enjoy a nice cold beverage of your choice, such a beer, and be proud of your accomplishments. Then find your next race and work to beat your time... that way you can enjoy 2 beers, 1 for finishing and the other for beating your previous time ;).