For Regular PC Users

Step I :-

After every 20 minutes of looking into the computer screen, turn your 
head and try to look at any object placed at least 20 feet away. This 
changes the focal length of your eyes, a must-do for the tired eyes. 

Step II :- 

Try and blink your eyes for 20 times in succession, to moisten them. 

Step III :- 

Time permitting of course, one should walk 20 paces after every 20 minutes
of sitting in one particular posture. Helps blood circulation for the entire body.