There is no end to downloadable guides on Adsense - and most of these guides are well worth their money in my opinion. But most of these guides all cover the same basic principles. I don't want to spend too much time on things that you already know, so I'm going to cover the most basic principles quickly. These basics tend to apply to both forums and regular websites.
First, always test and record your changes. This is a rule that applies to anything that you do with your website, not just to Adsense optimization. Never assume that you know what is going to work best on your site - let your visitors decide that for you. You should test ad sizes, colors, formats and locations to see which perform the best. If possible, setup split testing on your site and track your results using Google's channel tracking.
Be sure to give each version of your ad enough time to get real results. You should aim to give your ad at least 500 views (preferably 1,000 views) before making any changes. 100 ad views is certainly not enough to make any good judgment on.
Adsense optimization experts seem to agree that overall there is one ad size and color combination that seems to win most split tests. This ad size is the 336 x 280 ad size, with a blue headline (#0000CC), black text (#000000), and a dark grey url (#666666).
Although this is not always true, often blending your ads appearance into the content of your pages is a good way to increase your clickthrough rate. The reason behind this is simple: people have developed ad blindness. In general, if they recognize something as an ad, they will simply ignore it and move on to what they believe to be regular content. By blending your ads into your site, your website readers will be more likely to read the ad, and subsequently click it.
Now be sure to never "trick" your website users into clicking on an ad. Never use text that would mislead the person into thinking that the ad is part of your content, and never tell the user to click the ad in any way. Also, Google no longer allows publishers to place images next to their Adsense ads in a way that would make the images look like they are part of the ads.
