Warm Up and Cool Down
Warm up for five to 10 minutes before your workout to prepare your muscles for exercise. Also be sure to cool down for the same amount of time at the end of your workout.

Boost intensity
Try fartleks, a Swedish term that describes a form of exercise in which you alternate between a fast and slow pace. This challenges your body to work harder for certain amounts of time—marked by the distance between objects rather than minutes—followed by a recovery period.

To do them, pick an object in the distance, such as a mailbox or light post, and run as hard as you can until you reach it, then jog easily for a few minutes to recover. Aim for 30 seconds to one minute of fast running and two to five minutes of slowing down. As you improve, increase to running two minutes fast, then four minutes slow. Repeat five times.

Indoor option: On a treadmill, do the fartleks described above, but use music as your guide. Run fast for one song, then jog slowly for the next, and repeat five times. For variety, run fast during the chorus of a song, then slow down for the rest. This also works on an inside track.

Build strength
Tackle hills, which challenge your quadriceps, hamstrings, calves, and buttocks. Find a hill along your route.

Run up, taking small steps while gradually increasing your speed until you're going as fast as you can at the top—raising the speed will make your muscles work harder. Run downhill taking long, slow strides to catch your breath. Repeat three to five times.

Indoor option: If you're running on a treadmill, increase your incline to the highest level, and run as hard as you can for one minute to simulate hills, then return to a flat incline for two minutes. Repeat three to five times.

Quick Tip: When running uphill, gaze up to where you're going, rather than looking down at your feet. That will help you keep your head up and maintain good posture.

Improve flexibility
The following stretches prepare your muscles for action and loosen your joints. Do them after the warm-up and after your cooldown.

Hamstrings, hips, lower back, buttocks: Lie on your back, and bend right knee, holding the thigh with both hands. Pull your leg toward you gently to feel the stretch in the back of the thigh. Next, bend the left leg, and bring your left heel behind right knee (left knee will be out to side), and gently pull both legs toward your body to deepen the stretch.

Hip flexors (front of hips): From a standing position, bend down and place palms on the ground on either side of your feet. Now bring left leg straight behind you, with toes on the ground and heel lifted, keeping the right leg bent with your foot in between hands. Make sure the front knee doesn’t go past your toes as you stretch. Switch sides. This is a difficult stretch; you may need to work up to it gradually. Modify it by keeping your left knee on the ground.

Calves and back of leg: Start sitting on floor with legs extended. Bend left knee, so left side of your leg is flat on the floor and bottom of left heel faces right thigh. Flex your right foot, and place hands on your right calf. Now lean torso toward right leg until you feel the stretch in your calf and hamstring. Switch sides, and repeat with other leg.