The positioning of your Ads relative to the rest of the content is important in order to adequately emphasize the Ads. However, positioning of the Ads is also dependent on the size and shape of the AdSense Ads. Though shape and size are customizable too, large size Ads are generally preferred because they help increase the number of Ad impressions you can get. However, sometimes the structure of your webpage might not allow a big size Ad. In such a case you would need to strike a balance between the size of your ad and the best positioning for it. A number of website owners use other properties in order to make the big size Ads appear smaller e.g. they might use the background color of the webpage for the background and border of the AdSense ad thereby making it look smaller than it actually is (besides achieving the blending effect, of course).
Position your AdSense Ads in such a way that they look in-place with the general flow of content on your website. You can even position a block in the middle of the content in such a way that it adds value to the content (while it also serves your purpose of increasing the AdSense revenue through clicks) e.g. you could add an AdSense Ad block just after a statement that points to resources for a particular task and your AdSense Ads could possibly form some such resources. Placing the Ads just above the heading of an article or just after the end of the article is another good way of positioning your AdSense Ads.
So, position your AdSense Ads intelligently and you would be in for a party much earlier than you would have expected.