Your body reflects the way you have used it and so when we spend a lot of our day at computers we can be negatively shaped by poor ergonomics. What are the key aspects of this activity?
We know that people generally sit for too long. The recommendation is 20 minutes and then you should get up and move around. Research by Kallings et al can be found here which shows sitting more than 75% of your time at work is associated with neck / back pain and poor general health.
When you use more than one screen, try to even the strain on your neck and always have your screen high to keep your head straight.
Your elbows should be by your side and your chair should support a neutral position of your spine.
Laptops should be supplemented with a external keyboard and mouse or eslse with a monitor.