I have a job where I must sit at a computer a lot. Sitting is terrible for your body. In order to counter this, I frequently stretch. I will do a shoulder stretch by pulling shoulders slight forward then slightly up and then back a bit. This pulls then straighter. I lift my neck up and sometimes assist with my hands to do this ..gently.
I may also get on the floor and do a curve up ( sphinx) stretch. You may not be able to use the floor but you can place your hands on your hips ..and curve your back a bit to relieve the tension there.
Also while sitting- be sure to sit tall, don't slump.
A good workout after work will help erase the problems sitting can cause. These also help!!