Here are some advice on google adsense ad placements.

• Use a large rectangle and try to wrap your content around it
• Avoid using borders in your advertisement
• Try to keep the look of your advertisement and site almost the same
• Make your website keyword rich so that the right advertisements are shown

If you do a rectangle, remember that you may not put any more on that page, google's limit is 4.

I agree with those, but if they are what is used to run the site. They should be clear and easy to see. Although they shouldn't clash that much with the site, and should blend like stated.

Also, you should never place your ads on the home page and the main navigation pages. Such pages are broadly themed and therefore, the ads are never targeted. This will result in less users clicking on the ads.

Place the ads on left side of a webpage in a skyscraper. It could increase the click through rate. But blending the ads with the site is a must because if the ads appear in a different color compared to the links within the site then visitors will realize it and avoid clicking them.