Don't pay for link exchanges. This is what just got JCPenney in trouble; the company's SEO firm was paying all sorts of sites to add links back to Penny. This can work well in the short run, of course, because the number of links pointing to your content is one of the most important factors that Google employs to weigh your site's value. And that's why it's such a serious crime to fiddle with it.
Don't duplicate your content. One way Webmasters sometimes try to bolster their ranking is by duplicating content across domains or subdomains. Alternately, a similar strategy is to scrape content from other sites and reproduce it with little to no changes inside the framework of a different site.
Don't do keyword stuffing. That's when you load pages with keywords in a way that doesn't help visitors read or make sense of the content, but instead is just there to be crawled by search engines. For example, if you've ever thought, "we could put keywords in a light color in the background so no one would see it," you're conspiring to commit keyword stuffing.
Don't rely on negative feedback. You know how there's no such thing as bad publicity? Some Webmasters literally bank on it -- bad reviews and negative feedback lead to lots of external links, which can enhance your site's prominence in search results. Almost unbelievably, it kinda works. That's why Google recently tweaked their algorithm to try to bury results for low quality sites that employ these practices.
Photo courtesy Flickr user phphoto2010
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