Google recently held a webinar for AdSense publishers. They gave out some adsense optimization tips that they have gathered over the past few years. The transcript is pretty lengthy, so here's the summary:

• Ad Location - "the middle, above the fold location perform best." Also "if you have an article page with a long body of text, the bottom of that article is actually pretty successful"
• Ad Formats - "the top three formats are the 336x280 that you see on the page; the 300x250 medium rectangle; and then the 160x600 wide skyscraper." Additionally "the wider ad formats are doing better than the other ones and the reason is that they actually take up fewer lines. And so with every additional line, you have a chance of losing that interested user."
• Ad Colors - Pick colors that blend well with the site. Matches the background color, and compliments the site. Make them feel like a part of the site. They give an example where a customer went from blended background to yellow, and clicks dropped 65%
• Ad Blindness - if the colors stick out too much, readers may immediatly identify them as ads and not even look at them. Also frequent readers may stop reading ads so you could alternate positioning and colors to get their attention. "The more you blend in with the site, the less chance that ad blindness will occur."
• Experiment - this was a big theme in the webinar echoed by all experts. Use channels to test different colors, positioning, and formats to find out what works best. They show that you can more than double your revenue just by finding the right color, position, format combo.
• Image Ads - If you want to maximize revenue they recommend turning them on. I personally disable them in my account, because I find them too distracting/annoying to the user. Yes you may increase your CPC, but you will probably decrease impressions over time.
• Link Units - Don't take up much space, and also "allows the user to refine what they're interested in. So if they may not be interested in specific ads on your page, they might be interested in a particular topic, and by clicking on a link unit and a link in the link unit, they'll be able to specify that they're interested in that specific topic and get a lot more options and variety on the ads that might appear." I also bet google remembers what they click on and then tries to generate better ads for the page... just my speculation.
• AdSense For Search - You can use this for your site search, and you get a percentage of ad clicks.
• Focus on Content - Duh!
• Don't click on your own ads - One of the callers asked the question "I was just noticing that someone asked about clicking on their own ads and it says you're not supposed to. And I don't remember reading that. And I occasionally do click on the ads... So is that detrimental in some way?" - I can't believe they said that to google. Google's response was: "Yes, that's sort of chief among the terms and conditions".
• Impression Counter - Google confirmed that Page Impressions are counted when a public service ad (or alternate ad url or color) is displayed.
• Your site is unique - all these things may not matter, the best location, format, and color is different for every site. So again, go experiment.

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