Download a printable pdf file of this self-care technique here: Hamstring Stretch
This video shows how to do a facilitated stretch for your hamstrings using a stretching strap.
Be sure to have you arm high so that you are not pulling down with the strap. A downward pull can stress the knee, causing or aggravating meniscus problems.
Lying face up, wrap the stretching strap around your ankle, then bring your leg up as high as you can with your knee straight. Pull on the stretching strap, with your arm held high, to help maintain the stretch.
Try to bring your leg back toward the table using just 10% of your strength for 10 seconds, against the resistance you provide with the strap. This will fatigue your hamstrings so they will stretch further.
Now bring your leg higher using your own power, not pulling on the strap. This will engage your quadriceps and cause the hamstrings to be inhibited, allowing a further stretch. Once your quadriceps have engaged you can pull on the strap to get a further stretch.
Facilitated stretching is the most effective way to stretch as it works with two effects, first fatiguing and then inhibiting the muscle being stretched.
To do the stretch you need a stretching strap, which can be found at http://simplefitnesssolutions.com/stretch.htm