A friend (non yogi) came to me for a few yoga moves to do when his low back "needs stretched out". He is your average muscular, several years of weight lifting type of guy. I'm guessing his stretching routine has been little to none. I had difficulty finding something that wasn't too advanced, so here are a few key poses to get you started. If something doesn't feel quite right, rest or move on to the next posture. As always, if you have acute pain, please get your doctor's OK before attempting any of these poses.
Child's Pose - Your knees can be wide, or close together, with feet close together. Your hips will be moving toward your heels, but if they don't reach, just let them hover, or use a pillow as a prop. Arms can be stretched overhead, or stretched along the sides of your legs. Concentrate on lengthening your spine, and softening any tight areas. After a minute lay on your belly, using your stacked palms as a pillow for your forehead.
Locust Pose - From your stomach, reach long through your inner ankles, legs slightly lift off the floor, while attempting to keep as much length in your spine as you can. Head can remain down, or hover your arms and head off the floor. Keep the length between the head and feet a higher priority than the degree of backbend. Hold the pose as long as you can, or flow slowly up and down, pausing at the top and bottom of the movement. Continue for a minute.
Cat/Cow - Move to all 4s and find a neutral spine (not sagging down or rounded up). On an inhale, lift your chest, gaze, and hips while you exaggerage the arch in your lower back. On your exhale, round your back (like a halloween cat). Move through these stretches for a minute.
Downward Facing Dog at the Wall - Bring your hands to hip height at a wall and step your feet back until your back is flat like a table, and your feet are under your hips. Keep your knees soft at first. Press your second finger strongly into the wall, and move your hips back and slightly up to create a lot of length in your back. Try not to arch your upper back. You can straighten your knees if you can do so while maintaining the feeling of length that you've just created in your spine. Start at a minute, and work toward longer holds.
Reclining Pigeon Pose - Lay on your back with your knees bent and feet on the floor. Cross your right ankle over the left thigh. If you feel a good stretch here, stop. To intensify the movement, grab your left thigh and bring it toward your chest. Don't go so far that your hips lift high off the ground. Hold for a minute, then repeat on the other side.
Reclining Banana Pose - OK, so I made the name up. From your back on the floor, reach your arms overhead while reaching your legs long, and keep the length. Make a banana shape (and stretch the side body) by bringing your head and shoulders to the right while bringing your feet to the right. You have the option of crossing your left ankle over your right. This should stretch the left side body. Hold for a minute, and repeat on the other side.
Legs up the Wall - Lay on your back with your hips on a firm pillow, yoga bolster, or folded blankets. Let your feet and legs rest against the wall. Close your eyes and allow yourself to relax for 2 minutes or more.