After many years of experimenting, I have found the way how to earn real money with Adsense.
All my experience can fit into five tips:
1. Place only one ad per page (336x280px or 250x250px) (if there are more ads - click price will be lower)
2. Blend ads into your web page design, same color of navigation and other links
3. Place ad on zone which is visible to user while page is loading (Google: heatmap keyword)
4. Do not duplicate or copy content, Adsense bot is very, very sensitive to duplicated content
5. People will last longer on pages with white or non-dark background