Dead easy.

I implemented this tactic myself recently on one of my sites and my CTR has gone up 300% and it hasn't been 24hrs yet. Needless to say I'll be spending sometime making changes to my Adsense ads across my network of sites.

What is it?
Sorry, can't resist a little intrigue.

It's very simple.

Using the Adsense Leaderboard banner 728 x 90 I added small images/photos above each ad at 140 x 100.

These photos are broadly related to the ads and draw the eye of the visitor to the ad. Which the ad alone maybe would not do. Once the eye is drawn your visitor will be much more likely to read the ad text below the image and in turn they'll be more inclined to click.

Google already knows of this tactic and I know a number of people have approached them via email before implementing the images. Obviously nobody wants their account suspended. The good news is Google are fine with it, for now at least. Although a few warnings have gone out with regard to animated images not being appropriate. So no Flash or animated gifs!

You can view this in action on one of my sites -
http://www.how-to-make-money-online.info

You can't fail to see it at the top of the page.

Now I hope this is new information to you. If so I know it's going to be damn useful. :) And most of all profitable!

The benefit of this over Google's own Adsense 'image ads' is that you choose the image for one and the basic text ad appeals for another. As I'm sure you are aware text ads work better than image ads. Combining them together in this way seems to work btter than either one of them would alone.

There's also a major boost in the fact that you are able to select the most relevant image for your site content and current adsense ads.