Go wide and get rich (media)
If you've just recently started with AdSense, there are two format-related tips I would instantly recommend. The first is to enable both text and image ads, which will increase competition among ads to appear in your ad units and may result in higher CPMs. Second, use some of our wider units, such as the 160x600 wide skyscraper, the 300x250 medium rectangle, or the 728x90 leaderboard. There are more rich media (image, flash, video and gadget) ads available in wider ad formats, and wider ad units are the preferred formats for advertisers looking to target your site. Again, increased competition or your ad space will help you maximise your earnings potential.
Channels are powerful reporting tools, sometimes overlooked by new publishers. They allow you to view the AdSense performance of a site, a specific page, or even a specific ad unit, which can help you see where your ads are performing best. You can name these channels, give them descriptions, and then define them as ad placements so that they are visible to AdWords advertisers.
As top AdSense earners will tell you, when it comes to earning with AdSense, the most important thing is a policy-compliant site with good-quality, original content. Such sites attract users, relevant ads and, ultimately, revenue.
Finally, we constantly maintain online resources like our AdSense Help Forum, Newbie Central, and our Known Issues page to share useful information with you. We hope you'll use them to make the most of AdSense.
Link - from Inside AdSense
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