I did this research myself with some webpages and it was really worthy. As a writer I write articles and submit to ezinearticles to get traffic as well as external links. I tried writing articles of good quality of 300-400 words and I also wrote some articles with spelling mistakes and without a proper flow. I found out that articles with spelling mistakes and bad flow got me more $'s per click.
I also tried to research on the designing part of some webpages. Webpages with dull look got more clicks than that with bright ones. The placement of ads is also one of the most important part in getting clicks, as described by many google adsense Guru's it is best to have your adsense ad on the top left side of the website. Make sure you have the maximum google ads on your website as you are not gonna lose anything if you have maximum ads on the site.
I also tried putting small images on top of the google ads and the click thru's were really great.
If you want to get more revenue per click then you can opt for google image ads. You get more $'s per click on image ads.
If you have lots of articles, then it is advised to make sure you have a google ad on the top left side of the web page. You can also have 2 google ads placed in the center of the articles, which would get clicks.
To learn more visit: http://www.TotalAffiliates.com