The next two poses, Cat and Cow, are often done together in sequence. Together, they stretch the back and shoulders, and are a great exercise to do every day, whether you're practicing a full yoga routine or not.
Start on your hands and knees on the mat, knees below hips and palms down, below shoulders. As you exhale, begin to lower your head and round your back, lifting your abdominal muscles up and in. Your head should release toward the floor, but don't strain it by tucking all the way into your chest. On your next inhale, come back to a neutral "tabletop" position with a flat back, or continue the flow into Cow pose.