meta tags

Meta tags are HTML elements used to provide structured metadata about a web page. Such elements must be placed as tags in the head section of an HTML document.

General Rule of Thumb:

• Title: 1-12 words max (with page keyword)
• Description: 5-24 words max (with page keyword)
• Keywords: 3-12 keyword phrases, individually separated with ","
• Meta tags must reflect page content
• Each page should naturally optimise one keyword (with multiple phrases) and be reflected in the meta tags
• Keep it simple

title tag
The W3C states that the Title Tag is the most important element of any quality web page, and the search engines obviously agree.

A good title is generally a 8 to 10 (12 max) word description of the page contents. Try to include the relevant keywords or keyword combinations that occur within the pages subheadings and text. Using descriptive titles not only benefits search engines, but it also makes logical sense, gives the page a more complete feel, and is a huge benefit to users browsing the page using assistive technologies.

Basically it is the text that appears on the top bar of the browser. Make it readable to visitors, not search engines. Using words in your title that people are searching for can improve your search engine placement. The title should not include stop words such as of, and, it, for.

description tag
A short, plain language description of the document, usually 20-25 words or less. Search engines that support this tag will use the information to publish on their search results page, normally below the Title of your site.

Make your meta description as compelling as you can, as your description often is the difference between getting your listing clicked on in the search results or your competitor's site.

The meta description tag should contain multiple keywords organized in a logical sentence. Place the keywords near the beginning of your description.

Search engines vary in their preferred length for meta tags. Try to use the smaller number, 150 characters, for your site. Never make your description tag more than 250 characters long because some results pages will cut it off.

keywords tag
Keywords are used by some search engines to index your document in addition to words from the title and document body. They are typically used for synonyms and alternates of title words. Make sure to only use keywords that are relevant to your site.

(http://www.accessibility101.org.uk/websitedesign101/definitivemetatags.htm)