Oh, and hit random keys on your keyboard so they will think your actually typing. You could also open and close your desk drawers a couple of times to make it appear you are actually looking for something you need to complete your work.
Also when you leave your desk, leave papers scattered all over the place so it looks like you just took a quick break from your work to go to the bathroom or to get another quick cup of coffee to sip on while you work. Keep these excursions away from your desk short, brief, and infrequent!
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. But on second hand, wouldn't it just be easier to ACTUALLY work rather than doing so much work just to appear like you are working? 
