Simple tips to prevent neck pain (which often refers into the shoulder blade, upper trapezius and shoulder):
1) Sit with a lumbar roll (this will support your lower back curve which will correctly align your head/neck position)
2) Set you office space up so that all documents, computer screen etc is at eye level where possible. If you do a lot of laptop work you need a detachable keyboard as it is impossible to sit with good neck posture otherwise.
3) Regularly perform Retraction, or if not limited by any pain or discomfort, Retraction-Extension (as in the video) x 5 every few hours of sitting or reading or when you become aware of strain or stiffness developing
4) Hold iphones/ipads/books up at eye level when reading. It is frequent or sustained looking down, or poor posture where the head protrudes forward that causes the issue over time