Use of meta tag in HTML

In HTML the tag provides metadata about the HTML document. The content of meta tags generally describes information about the HTML page which usually cannot be represented by any other HTML tags. In addition to that, the meta tag can also be used to emulate an HTTP response header. The META elements can be used to include name/value pairs describing properties of the HTML document, such as author, expiry date, a list of keywords, document author etc.
The tag is used to provide such additional information. This tag is an empty element and so does not have a closing tag but it carries information within its attributes.Metadata will not be displayed on the page, but will be machine parsable.
Even though the description meta tags have no effect on search engine rank, they do appear in search results.
How do you write the ideal meta tag:

• tags always goes inside the element
• Metadata is always passed as name/value pairs.
• The content attribute must be defined if the name or the http-equiv attribute is defined. If none of these are defined, the content attribute cannot be defined.
• Make sure any given meta title and/or description is not duplicated across multiple pages
• Meta tags are kept clear, short and precise
• Avoid using quotes as Google has been known to cut the descriptions off
• The focus is on readability, relevance to that page and creating genuine appeal
• Be relevant and accurate with your description of the page’s content
• Emphasise credibility and emotional connection/engagement
• Consider your brand strength and be sure you mention it clearly, to achieve greater stand out
• Connect with your audience via brand consistency and focus on the desire to click

source:http://www.criticone.com.au,http://www.w3schools.com/