Also see: 9 Ways to Help Beginner Runners
Set a new PR.
Also see: How to Run a Faster Marathon
Tips for Running Faster
Run for a cause.
Also see: Charity Running Groups
Also see: 7 Ways to Stay Injury-Free
Volunteer at a race.
Race directors are always looking for people willing to donate time. To get involved with a local road race, contact your local road runners club. Or, if you want to volunteer for a big event, such as a marathon, check out the volunteer opportunities section on the race's web site. Seeing the smiles of appreciation and gratitude from runners will definitely make it worth your time and get you motivated to train for your next race.
Try a new distance.
Also see: How to Find Local Races