The Glute Ham Raise (GHR) is one of my favorite lower body assistance movements for building the hamstrings.
Start with your body in a horizontal position, toes pushed against the platform, and knees a couple inches behind the bench.
Drive your toes into the platform and curl your body up using your hamstrings. Squeeze your glutes tight, keep your abs tight and chin tucked.
Avoid breaking at the hips and arching the lower back to come up. Maintain a neutral spine — keep a straight line through your knees, hips, shoulders, and neck.