Yeah, size matters, but so does placement…particularly as far as Google AdSense ads are concerned.  Use the skyscraper format for ads, putting them in the margins as opposed to banner ads across the top or bottom.

Well, guess how much difference that can make? Poorly placed ads, such as banner ads down at the very bottom of the page, might have a click-through rate of about 2.3% on a good day.

But well-placed ads, such as a nice skyscraper ad in that critical upper-left quadrant we talked about, can have a click-through rate as high as 40%.

And that’s for the same ad that was poorly placed.  Yes, the very same ad can have a click-through rate of an abysmal 2.3% or an awesome 40%, depending on where you place it on the page.  It has nothing to do with the ad itself and everything to do with where you put it.

Another good tip to maximise click-through is to massage the colors of the ads so that they fit in with the colors of your site.  Ads that are seen as “fitting in” get more clicks than ads that clash.