Vertical and small ads

Place vertical ads on the right side of the page. Most surfers
tend to use their mouse to scroll down on the right side of
the page; so placing your tower (or vertical) ads on the right
gives it a higher chance of grabbing the visitor’s attention.

Small Ads
Studies say that the upper right hand corner is the first spot
on your site that someone sees. Try placing your small ads
at the top right hand corner. Grab the visitor’s attention
when they first come to your site with your AdSense ads. If
an ad interests them, they’re still going to browse through
your site, but they will come back to click through that ad.