Warming Up
Stretches should be held at the point when mild tension is felt in the muscle, and should be held for 20 to 30 seconds. Under no circumstances should you bounce or lunge when stretching. You should not feel any pain while stretching.
Quadriceps
Holding on to a wall for support, hold the foot (furthest away from the wall) behind you so that you feel the stretch in the front muscle of the upper half of the leg (quadriceps).
Keep the support knee slightly bent, knees together and bottom tucked under. Repeat the stretch for the other leg.