Six AdSense optimization tips for forums
by Sandra - AdSense Publisher Support

1. Format is important for multiple ad units
Placing a skyscraper above the fold on the left side of your forum seems to produce slightly better performance than other positioning. However, when using multiple ad units throughout the page our horizontal bias still favors the leaderboard. See the Forum Heat Map below for more details.

2. Display your ad units where repeat users will notice them
A leaderboard at the very top fits nicely next to the logo, but forum regulars tend to skip the header and go straight to the meat of the thread. Placing your ad unit above or below the first post can be more effective.

3. Place a leaderboard immediately after the last post
This provides users who make it to the end of a thread with a ‘next step’ when the content ends. If you place it after the footer, though, folks will move to the next thread before they even see the ad!

4. Use horizontal link units
Link units offer a wider range of relevant topics for users to browse. A horizontal unit can be placed near the top of your forum just below the header.

5. Opt-in to image ads
Supporting image ads increases the pool of ads –particularly cost-per-thousand-impression (CPM) ads – bidding to display on your site. Since forums tend to have lower click-through rates (CTRs) than other types of sites, CPM ads can improve revenue without the need for clicks. Please remember, however, that CPM ads come in both text and image formats.

6. Be sensitive to your forum community
Forums are highly interactive, so be sensitive to your users when implementing your AdSense ads. Be sure to blend the ads nicely, so they don’t appear overly intrusive –but don’t blend them so well they mislead your users! Every forum site is different and you know your community best, so as always use your own judgment to create the most positive experience for your users.

The last tip, to make sure the adsense blends in with everything, doesn't just apply to forums. Make sure adsense blends in with your site all the time.

thanks for the advice, I am going to go sign up for one right now and use all the tips from this forum thread. I also wanted to know how to keep it up for a long time.

last last steps makes sure you test, test, and more test. It always change constantly.

Does adsense really work for forums? I would think that the user is more interested in replying to the message, rather than focusing on the surrounding ads.

u r true lol
in my forum i earned a whooping 2$ this month from my forum www.hiifii.com/forums

Thanks for the tips, my sites almost about ready to go up and im hoping that once i get some traffic coming and going i can get alittle of that Ad Sense money i've been hearing so much about lol

Not just hearing, i recommend you to try it out also.
Its the Best program , but only until you dont break the TOS