As the muscles in the spine can get very tight, including an upper back stretch into your flexibility routine will well be worth your time. Far too many of us carry a lot of stress in our body as we go through our day so finishing up the night with an upper body stretch is a good idea. Don't think that this exercise is one that you should only do after a workout.
One very good upper body stretch, which is actually more intended for your triceps but will also target the spine, is done by crossing one arm over the body. As you do this take your other arm and gently pull the hand further so you feel a nice pull near the very end of your shoulder as well as into the shoulder blade area. If pulling on the hand is uncomfortable, you can also pull on the elbow slightly. Either way will work, it is just more a matter of which method you prefer.
Another exercise to perform is a corner stretch. To do this stand in front of the corner of a wall, one hand placed on either wall. Next press inwards so your shoulder blades move close together and your body comes near the wall. This would be the contraction portion of the movement. After holding that, curve the other direction so there is a bend in the shoulders and spine and you are now extending the muscles and joints.
To get started in the last exercise you should perform, lay stomach down on the ground. Then with your hands in front of your shoulders slowly press the top portion of your body upwards, without letting your ribs come off the floor. Note that when doing this, you are not aiming to target the stomach muscles at all and you should not stretch up so much that you start feeling a pull there. If you do, decrease the distance you are moving in.
So make sure you don't forget to do a few exercises for this area of the body both at the end of your workout and at the end of your day. Not only will you feel better physically but you will also improve your posture in the process.