After using AdSense for a while you must have begun to ask yourself if there's anything you could do to improve your AdSense based earnings. But before you go on experimenting with this and that setup you have to realize a couple of things about positioning.
The first thing you should know is that there is no universal position that is guaranteed to improve your earnings. That being said, the part above about experimenting is meant to be taken literally. You have to try as many setups as you can to find the solution with the greatest benefit.
But, of course certain places usually work better then others. Of course, Google recognizes this and they publish a "heat map" of how much revenue ads placed in certain portions of the page can bring you. Experimenting is often the best way you can find, what suits the sub conscious mind of your audience.
Generally the most profitable ads are placed within the main content, generally right above it. But this is by no means a rule and there are some exceptions to it. One known exception is having a news site or something similar to a new site.
If this is your case, you will often find that you generate more earnings by placing your ads at the bottom of the content, right before comments begin. This is because as users finish reading a story, they have a short moment where they're looking for something more to do. And your AdSense ads can offer them that something.
Also, placing ads to the left side of your page seems to work better almost all the time. Of course, this is logical because text is generally written from left to right (unless you come from certain countries where it's the other way around).
People will finish a sentence and return their eyes to the left position, which means they have a higher chance of spotting your ads.
Also, there's a bit more to this then just having ads visually in the right place. If you have more then one ad you have to worry about where they're located in the code as well. And there's a very good reason for this concern.
AdSense fills the ads in the order it finds them in the source. That means that if the first add you have in the code isn't the one generating the highest revenue, you may soon start to lose money, rather then earn more.
This is because if AdSense doesn't have anymore ads it will supplement your space with public service ads or just leave it blank altogether. That means that, if you're unlucky, you could end up with your most profitable locations not having any good ads at all. To supplement your revenues
There are other issues with how many ads you should place in your site. The problem is that if you have too many, rather then generate more income, you'll have a lower click through rate, as visitors tend not to follow ads from the places where these come in excess.
You have to constantly keep track of how the users interact with your site. Keep an eye out for where the visitors will be looking at your site most. This is generally the place where you want to use your first ads. Also try not to place ads in annoying positions as that can guarantee a lower click through rate.
Of course, you always need to have ads that blend in with your content and generally don't make the visitor's presence on your site an unpleasant one. The key is providing an enjoyable experience for your visitor, whilst generating revenues from their exploration.
And again, ultimately the best revenue will be earned through a lot of experimentation. Be sure to use AdSense's channels feature and be on the look out for how certain ads in your pages are doing whilst altering the positions to better supplement your earnings.