Figure 4 Stretch
This is one of my favorite stretches for the low back. I recommend doing this 2+ times per day. Hold the stretch for 15-30 seconds and repeat 2-3 times. The analogy I have repeatedly used is to look at stretching like brushing your teeth. It should become a daily routine.
Lay on the floor on your back. Bend both legs keeping your feet on the floor. Bring your left leg up and rest the outside of your left ankle against your right leg just above your knee, as if you were crossing your leg. Next, using both hands, grab the thigh of your right leg (or if your limber the front of your lower leg below your knee) and pull your leg towards your body, holding for 15-30 seconds. Repeat with the right leg. Repeat cycle 1-2 more times. One important thing to note with this stretch is to keep your head flat on the ground so as not to strain your neck.