Placing Ads in the right spots on a blog post or page can increase profits ~30-60%.

You want to place the ads as high and as centered as possible.
The larger the ad, the easier it will be noticed.
Google allows you to display a maximum of three ads on any one page at a given time.

I've found that it's best to place the largest square ad(336x280) centered just below the blog post title. Place the next ad one full screen down the page. Pick the largest ad size you can that is small enough to fit in the WordPress sidebar. If you don't use WordPress for your website, just center another 336x280 ad within to post content. Look at your page and make sure it's aesthetic and intuitive enough to read. If your page is too annoying and hard to read, visitors will bounce. You may have to use a smaller ad for the second placement, especially if you don't have a sidebar to place it in. Place the last ad on the bottom of the page just after the post. I haven't noticed any significance regarding the type/size of add places on the bottom of the page.
The idea is to space the ads far enough apart so that they are never seen together. As the reader scrolls through your important post, he will notice the pretty ad popping out among the text.

I also notice more clicks from image ads. I'm not sure if image ads are just better than text ads. I tend to think that image ads stand out easier on a blog page predominantly displaying text. I can assume that text ads are more apparent on pages made up of mostly images. Contrasting your ads from the content of your post/page lowers your chances of exhausting and annoying your visitor.

Another trick is to use Google AdSense for Search.

Note: to view this link properly, make sure you are logged out of AdSense before you click on it.

Most sites have a built in search option, but you can replace this with an AdSense Search option instead. You can configure the AdSense Search to search your site and display the results on a particular page within your site. I don't profit, but from AdSense Search, but it's still profit all the same. The Google Adsense for Search works just as good if not better than my default WordPress search script.