Aaron Wall has a good post about pulling out blogs from Google Supplemental Index. The methods listed include:

• Relevant and deep links
• Make longer posts and turn comments on
• Remove/downplay sitewide repetitive features
• Optimize your internal linking structure     

 As per commercial sites, Aaron says that you need to do all the above and in addition you should:

•     add an editorial element to your site to improve your sitewide authority score
•     enable customer feedback and reviews to get more unique content on your pages

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