A shoulder stretch exercise is a great thing to perform a few times for muscular tension release throughout your work day to prevent stiffness and soreness in the neck and upper body area. When we sit sedentary in a fixed position for so long it is not uncommon to become tense. If you were stop right now and consciously think of relaxing your shoulders, likely they would drop slightly. This goes to show that even just sitting there you are holding muscular tension. A shoulder stretch will make you aware of this muscular tension more often and help release it.
One simple shoulder stretch to perform is reaching your arms above your head, clasping your hands and then gently pulling backwards. This will stretch the frontal and lateral head of the muscle as well as your upper back and latissimus muscle.
Another easy one to perform is shrugging this body part up as close to the ears as you can, holding for a moment and then releasing while thinking of pressing down and back (shoulder blades together). This will get the blood flowing to the muscles, increasing oxygen delivery and relieving any tightness you might be experiencing.
The last exercise to do is started by standing with your side to the wall. Next place your arm against the wall so it is directly in front of you, the outside portion of the arm in complete contact with the wall. Begin twisting the body ever so slightly until you feel a pull in the lateral portion of the muscle. Note that you likely won't be able to twist very far but it should be enough to improve flexibility and relax this area of the body. If you can manage to move so that your stomach is nearing the wall (so your whole arm is still against it but your body is now rotated), that would demonstrate a very good range of motion. If you can't, this would be the goal you want to work towards.
So be sure to complete a few of these movements throughout your workday whenever you think of them. Additionally, they are great to perform at the end of your workout as part of your overall cool-down.