There's no single solution when it comes to positioning your AdSense ads. The best place to position your AdSense ads is where the visitor's attention is focused. Visitors interact with every site differently, depending on the type of site and how the navigation and features are arranged.

In general, there are some areas in a web page that visitor's eyes and attention are focused on more than the other. By compiling and analyzing the data of visitor's behavior, Google itself came up with the following “heat map”.

While Google provided the heat map above for AdSense unit placements, it's also applicable to any other PPC or affiliate ads. The heat map suggests that the darker the area, the more likely it is for visitors to look at your ads, and the better your ads will perform.

From the diagram, we can tell that the best performing ads are normally placed just before the site's main content and followed by other “above the fold” locations and the left sidebar.

Do keep in mind, though, though this is how it generally works for most websites, it might work differently for you. The general rule is to place it where your site's visitors are focused, and that could always mean near your site's content, which could be some widgets you have, article body, Youtube video, so on and so forth. Whatever it is, keep experimenting till you find the right spot. Also, keep in mind not to overdo your ad placement, and try to keep your site clean, uncluttered, and inviting.