That particular stretch is a great stretch. The type of stretching that you are looking for is called Developmental Stretching. Developmental stretching aims to improve your current level of flexibility. A developmental stretch is performed by increasing the stretch by a fraction until you feel the mild tension in the muscle again. Hold this position and when the tension eases repeat again. If the stretch becomes to painful,you have gone too far. You should be stretching with control and without bouncing. Bear in mind that a developmental stretch should be held for 20 seconds, to the point of tension(not pain), then you should relax into the stretch and aim to hold it for another 20 seconds. Remember to always breathe throughout your stretch and don't attempt to hold your breath at anytime.