Foam Rolling is a great rehab tool for all parts of the body. It can soften muscle adhesions leading to a faster recovery.
To foam roll the hamstrings, place the foam roller directly under the hamstring muscles. Roll back and forth 10-20 times. Be sure to concentrate on any "sticky" points. For more pressure, you can cross your other leg over the top. Turning your foot in and out will make sure you hit all areas of the hamstring. You can do both legs and once, but doing each leg separately provides more pressure on that leg.