Stand with your feet hip width apart, bend your knees and tilt your pelvis forward. Your body and thighs should be in a straight line. Hold this position for 5 seconds, you should feel tension in the front of your thighs.
Keeping your knees straight, bend forwards at the hip and relax your body downwards. Keep you weight evenly distributed across your feet and hold this position for 20 seconds. You should feel a stretch in your hamstrings, at no point should this stretch hurt. If it does, slowly come up out of the stretch to a position where you can feel a pain free stretch. Repeat steps 1 and 2, three times.