Many people think that the best position for the ads is in the highest place of your page. But think about it: when someone visits your site, what he wants? Read your articles! So why don't you put the ads right before the article? your visitor you read your text and than, when there is nothing more to do at that page, he will click on your ads! If you put an add in the middle of the article, there is a big chance that he even don't notice it. Or he will see it and won't click, because his attention is on he is reading. I put mine right below ther articles, with the same color or my page and even used the same font.
It really depends on the content of the page. I have a high bounce rate on a couple of pages as people are looking for something else when they find my page. Putting the ads at the top of the page meant they are more likely to click the ad for that particular page.
For the rest of the pages I normally have my ads at the bottom of the page (such as on gallery pages.)