Some say that meta tags have no effect on your ranking with the search engines. Well that is almost true except for one ” the description meta tag. Most search engines (including Google) do not in reality take it into account for ranking purposes ” yet ” many use it in their search results.
The content of the description tag is used more often than not by Google when it shows the results pages for a keyword. It uses only the first 156 characters though so make sure if you are using it to check the length of the text. If you do not check the length your text will be truncated and it will look funny.
So when you use a good description and a search engine uses it then it will help your click through rate. If your description is attractive people will click though more.
The meta tags should appear in the head section of the page between the head tags.
Google is a little rogue when it comes to using or not using the meta description tag. When it does use it you can have full control of what is displayed to possible visitors but it will often vary what it uses at will with sometimes it just plucking a piece of text from your page.
If you want to determine what Google displays then the very first 156 characters of text on a page should be highly controlled because if it does not use the description tag it will use this text.
If you have a flash site or just use pictures with a little text, you have a problem! We have seen Google pick up the alt text from an image and display this when it did not choose to use our description tag. This will tell you to ALWAYS have some text on your page even if it is only 156 carefully chosen characters (including spaces).