Pay attention to your posture.

Proper posture, especially if you sit and work from a chair for long stretches, is essential for good health.
• Adjust the height of your chair to minimize strain on your legs and back. Your feet should rest flat on the floor or a footrest and your thighs should be parallel to the floor.
• Be sure your chair has good back support. Sit upright in the chair with your lower back against the backrest.
• Don’t slouch, sit hunched over, or sit cross-legged when you work. Don’t use armrests to slouch.
• Take breaks from the computer every 20 to 40 minutes in order for your body to rest and recover. Working at the computer is very fatiguing on your upper body as well as your eyes. It’s important to get up and move around. Do tasks that aren’t computer-related.