If you have Google Adsense on your site, here is the best piece of advice I can give you: don’t put borders around your ads. I had a border around my skyscraper banner on the right here, so it sat in its own little box.
A friend told me to take the border off. I figured it couldn’t hurt to try it, so I made the border white, so it just fades into the background. Nothing else was changed. I did it in the middle of the month, so the first half was with the border, the second half without.
The result in terms of clickthrough rate? A seventy percent increase.