If your face is relaxed while running, you will feel a little bounce in your cheeks. Shoulders are another culprit. Hunching up those babies is hard work with no return for your effort. Concentrate on relaxing the shoulder area, particularly in the later stages of the workout. Arms should be carried low, moving back and forth to keep your body going straight.
Arm curls can be very impressive, but save 'em for the beach.
Top runners often relax in mid-race by dropping their arms down to their sides. Novice runners often carry their fists as if the expect Mike Tyson to come around the bend. The best way to keep your hands while running is with the thumb and fingers gently touching. Monitoring this part of the body often will really help keep you focused on relaxing during your workouts. Muscles that are loose will provide you with the strength and flexibility to train much more efficiently, and less chance of injury.