Google Adsense has released some optimization tips to help Adsense publishers place ads better and make more money with better click throughs. Though there are many articles about where to place Adsense ads, this heat map coming from Google itself is great as it must be after their study of research data related to highest earning best ad placements.
They say “This heat map illustrates these ideal placements on a sample page layout. The colors fade from dark orange (strongest performance) to light yellow (weakest performance). All other things being equal, ad placements above the fold tend to perform better than those below the fold. Ads placed near rich content and navigational aids usually do well because users are focused on those areas of a page.”
It is important to note that this is a general guideline. I have seen many sites change web design layout after release of this heat map. It reinforces the fact that top left hand corner is a popular target where the eyes sees first. The proximity to best performance near the primary content confirms the fact that content is what matters eventually.
Content keeps traffic coming back, and correct ad placement helps to keep your site running by paying the bills!