Let's see ... what I do here is set it up to show ValueClick ads instead of the freebie ones when it hasn't yet spidered the page. This way I make money either way. Also, due to Google's lack of stats reporting, you have to improvise. Try using leaderboards for a week or two. Then switch to skyscrapers, etc. It really takes that long to notice a trend because it fluctuates day by day.

Also, do some google searches for high-paying keywords. Integrate those keywords into the keywords and description meta tags of your site. Google's search engine doesn't use meta tags but AdSense absolutely does!

Disable AdSense from showing up in any forums that guests don't have access to. Google will spider the forum login page and think it's what your members actually see.

More when I think of it