Follow 20-20-20 rule:
Every 20 minutes, take an eye break and look 20 feet away for 20 seconds. This will give you a chance to blink and produce some tears and will give your eye muscles a chance to relax.

Blink often to refresh your eyes:
Because many people blink less than normal when working at a computer, dry eyes can result from prolonged computer use. Blinking produces tears that can help moisten and lubricate your eyes. Make a conscious effort to blink more often.

Consider using artificial teardrops:
Available over the counter, artificial tears can help relieve dry eyes that result from prolonged sessions at the computer.

Adjust your monitor
Position your monitor directly in front of you about 20 to 28 inches from your eyes. Keep the top of your screen at eye level or below so that you look down slightly at your work.

Keep reference materials nearby:
Place reading and reference material on a document holder beside your monitor and at the same level, angle and distance from your eyes as the monitor is from your eyes. This way your eyes aren't constantly readjusting.

Check the lighting and reduce glare:
Bright lighting and too much glare can make it difficult to see objects on your screen and strain your eyes. To check glare, sit at your computer with the monitor off. This allows you to see the reflected light and images.

Take breaks between long hours of work:
Take mandatory breaks lasting atleast a few minutes while working for long hours. Walk around, drink water and warm up your body with basic stretches.

Don't pound on the keys:
Use a light touch to type keys and to use the mouse. Keeping the muscles strained on input devices can cause muscle damage.

Adjust your chair:
Your feet should be flat on the floor (or on a slightly angled foot rest) with your knees bent close to or greater than 90 degrees. Your chair should support your legs without excessive pressure on the back of your thighs.

Reduce desk clutter:
Make sure that you can reach the most commonly used devices without stretching.

Breathe in deeply and slowly:
Once in every 10 minutes, breathe in consciously and slowly.

Take micro breaks:
Use short 10 second breaks to lose concentration and switch your body position to a different one.

Change the pace:
Try to stand up and move around at least once every hour or so. If possible, lean back and close your eyes for a few moments. At the very least, try to give yourself a five-minute rest every hour. Do other work, such as phone calls or filing, during this time.