There are many people who are making just $10 or $20 a month with Adsense even though they are getting 100s of visitors to their site every single day. The reason often is, because their ads are positioned wrongly. Google Adsense even goes as far as to give you a heat map explaining what the best positions on the page are for displaying your ads.
One of the best places to display your Adsense ads, is near your navigation menu. This is because people's eyes ALWAYS go there to have a look at the navigation structure of your site. They want to know where they are able to go next if it is not to stay on your page. It is therefore important to give them the option of clicking on one of your ads.
When positioning your ads, it is also important that they seamlessly integrate within your site. This means removing borders and making the background the same as the rest of your site. The truth of it is, that people do not like being advertised to. Taking this important fact into account, you should therefore make them look as much like the rest of your site as possible.