Last week I spent around 2 hours one evening tweaking the colors and placement of adsense on one of my WP-Answers sites, the site was receiving around 2.5% / 3% click through rate. Since that evening the average has been around 7.5% CTR! I bascially doubled the income of this one site over night - a lot easier change than doubling your traffic!
The main adsense block was 336 x 280, placed at the top left of the content with the content wrapping around it.
Changes I made :
I made the main body text slightly lighter to a shade of grey, rather than black.
I did the same with the page title, was blue; now the same shade of grey as body text.
I increased the padding around the adsense block to around 30pixels.
I made the background color of the adsense block a very pale shade of blue so it stands out against the white background and grey text around it.
The adsense title was made bright blue.
Any links near the top of the page were also made grey so the only blue area was the adsense block and thus stands out.
These changes for me have worked well on this site - standing out rather than blending in has made the difference.
Let me know what adsense findings you have made ?
Here is a diagram of what I did :
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