Use AdSense Tracker and Move the Ads

As you move the ads on your page or make other changes,
follow your CTR using your AdSense tracker. Note the
changes you’ve made and when you’ve made them. This
enables you to see what works and what does not work.

Move the Ads
Sometimes return visitors only see what’s new or what’s
changed. Move your ads from time to time, especially if you
notice your CTR dropping. More often than not, you’ll see
an increase again as those same return visitors notice
something in a different place and actually start to click
through the same ads they didn’t “see” last week.