ember - 4:34 pm on Feb 16, 2013 (gmt 0)
Ditto everything Netmeg said. I'd also add that well-designed pages are key to Adsense success. Original, well written content is the first thing but also how well each page is laid out matters. Design can influence behavior, and how Adsense interacts with content can influence how many people click and why.
Study the layout maps Adsense has. Install analytics and pay attention to where people click on a page and where they don't. Test to see if changing an ad's size or location or color increases clicks. So much of it is testing because each site is different.
We've been able to increase our revenue substantially just by paying attention to ad placement.