Correct sitting posture minimise body pain while sitting for long periods. Adjust your chair to a height where your feet are flat on the floor and your knees are in line with your hips. Sit up straight and make sure your hips are at the far back.
Apart from these chair etiquette, keeping your keyboard and monitor in front of you at several inches above eye level will help relax your neck and prevent stiffness. Be aware of your shoulders rising, especially during a stressful task, to avoid sore shoulders at the end of the day.