Google guidelines

The Google webmaster guidelines are a list of suggested practices Google has provided as guidance to webmasters. Websites that do not follow some of the guidelines may be removed from the Google index. A website experiencing problems being indexed or ranked well can find direction in the guidelines. Often websites are not following all of the guidelines and may experience a lower ranking in Google's search engine results or complete removal from the Google index. There are currently thirty-one guidelines which are split into four categories:

Quality: There are five "basic principles" and eight "specific guidelines" in this category. These guidelines are directed toward deceptive behavior and manipulation attempts that may lessen the quality of the Google search engine results. Violations of the quality guidelines are the most common reason of a website being removed from Google's index.
Technical: There are five guidelines in this category. These guidelines cover specific issues that may inhibit a web page from being seen by Googlebot, which is Google's search engine crawler.
Design and content: There are nine guidelines in this category. These guidelines give practical information to webmasters concerning the way their site is built and represent the most common unintentional mistakes that webmasters make.
When your site is ready:There are five guidelines in this category. These guideline provide specific direction for a webmaster who has created a new site and are also relevant for older sites which are not yet in the Google index
http://en.wikipedia.org/wiki/Google_guidelines