Google's SEO Quality guidelines - specific guidelines

# Avoid hidden text or hidden links.

# Don't use cloaking or sneaky redirects.

# Don't send automated queries to Google.

# Don't load pages with irrelevant keywords.

# Don't create multiple pages, subdomains, or domains with substantially duplicate content.

# Don't create pages with malicious behavior, such as phishing or installing viruses, trojans, or other badware.

# 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.