I learned this lesson over night. I recently got accepted with Chitika and quickly put an ad on my left sidebar. On the first day I had 360+ impressions, no clicks. Second day I had about 1,200 impressions, 0 clicks clicks, next day I had about 1,300 impressions, no clicks. At this point, I start researching about ad placement, I learned about the "above the line" and other simple tricks, such as putting ads near places with the most click activity. I then removed the left side bar ad and decided to put a small simple one under each article and then BAM, over night I started getting clicks. It completely makes sense now, but I'm still learning. I'm sure a lot of people know this stuff already, but if you feel like you aren't getting the amount of clicks you deserve try experimenting with ad placement, it helped me.