Following these guidelines will help Google find, index, and rank your site.
These quality guidelines cover the most common forms of deceptive or manipulative behavior. Webmasters who spend their energies upholding the spirit of the basic principles will provide a much better user experience and subsequently enjoy better ranking than those who spend their time looking for loopholes they can exploit.
Make pages for users, not for search engines
Don’t deceive your users or present different content to search engines than you display to users, which is commonly referred to as “cloaking.”
Avoid SEO tricks
A good rule of thumb is whether you’d feel comfortable explaining what you’ve done to a website that competes with you. Another useful test is to ask, “Does this help my users? Would I do this if search engines didn’t exist?”
Don’t participate in link schemes designed to increase your site’s ranking or PageRank
In particular, avoid links to web spammers or “bad neighborhoods” on the web, as your own ranking may be affected adversely by those links.
Don’t use unauthorized computer programs to submit pages, check rankings, etc.
Such programs consume computing resources and violate Google’s Terms of Service. Google does not recommend the use of products such as WebPosition Gold™ that send automatic or programmatic queries to Google.
Avoid hidden text or hidden links
Hidden links are links that are intended to be crawled by Googlebot, but are unreadable to humans.
Hiding text or links in your content can cause your site to be perceived as untrustworthy since it presents information to search engines differently than to visitors.
Don’t use cloaking or sneaky redirects
Cloaking refers to the practice of presenting different content or URLs to users and search engines. Serving up different results based on user agent may cause your site to be perceived as deceptive and removed from the Google index.
Don’t load pages with irrelevant keywords.
“Keyword stuffing” refers to the practice of loading a webpage with keywords in an attempt to manipulate a site’s ranking in Google’s search results. Filling pages with keywords results in a negative user experience, and can harm your site’s ranking. Focus on creating useful, information-rich content that uses keywords appropriately and in context.
Don’t create multiple pages, subdomains, or domains with substantially duplicate content
Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Mostly, this is not deceptive in origin.
However, in some cases, content is deliberately duplicated across domains in an attempt to manipulate search engine rankings or win more traffic. Deceptive practices like this can result in a poor user experience, when a visitor sees substantially the same content repeated within a set of search results.
Don’t create pages with malicious behavior, such as phishing or installing viruses, trojans, or other badware
If your site has been infected, it is generally because some vulnerability has allowed a hacker to take control of your site. The hacker may change the content of the site (for example, to add spam), or add additional pages to the site, usually with the intent of phishing (tricking users into parting with personal and credit card information). Alternatively, they may inject malicious code (malware)—for example, scripts or iFrames that pull content from another website that tries to attack any computer that views the page.
Avoid “doorway” pages created just for search engines
or other “cookie cutter” approaches such as affiliate programs with little or no original content.
If your site participates in an affiliate program, make sure that your site adds value. Provide unique and relevant content that gives users a reason to visit your site first.
Source: Webmaster Guidelines