There are a number of great stretches. I have found these work great
2-piriformis stretch - this stretches a muscle in the buttocks called the piriformis. Cross the side you wish to stretch leg over other (like sitting with legs crossed), and lean forward
3-hamstring stretch - the hamstring connects to the butt which connects to the low back. Keeping this whole chain stretched prevents a lot of injuries. Put leg up on small step or stool and reach down towards that toe. You can also sit and reach for your toes.
4-Lateral neck stretch - tilt head to one shoulder. Reach up with the hand and pull neck slightly to stretch more.