Most meta tags have no positive effect on your search engine rankings. Although these meta tags do not usually cause problems with your sites rankings, they are basically useless code that the search engine spiders need to crawl through before reaching the content on your page.
Meta robots tag explained
The most commonly misused meta tag is the meta robots tag.
Examples of how this meta tag looks aress:
<meta name="REVISIT-AFTER" content="1 month">
<meta name="ROBOTS" content="follow,index">
<meta name="ROBOTS" content="ALL">
There is no evidence of any search engines using these meta tags at all. Search engine robots will spider your page by default. Using a meta tag to tell a search engine spider to read all of your page or to return to your site after an allotted time, will not work. With all the sites indexed on these search engines, could you really expect a spider to return to your site exactly one month later just because you ask it to?
The only influence you can have on the spidering of your site is preventing search engine spiders from indexing a page. This is best done using a robots text file or robots.txt file, not by using meta tags.
Effective meta tags explained
As well as a Page Title, the only meta tags you need on your website pages are the meta description tag and the meta content type tag and although the meta keywords tag is not currently being read by Google, we include it as good practice, incase it is ever used again in the future, as it would be a nightmare to go through 500 sites and write a keyword tag for each page!
These should look like this:
<meta name="description" content="(website description)">
<meta name="keywords" content="(website keywords)">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
You need a description meta tag and you need to let the spider know the content type. There is no benefit to be derived from putting revisit-after and robots type tags into the head of the source code, other than these tags.
Common Head Tag Coding Error
Another coding error that is commonly made is missing out the doctype tag. This tag, which should be placed before the head tag and meta tags, is very important as it lets the search engine spiders know what version of html coding is used in the site. Your doctype tag should look something like this:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Some head tags are still important, irrespective of the misinformation that you'll find on forums all over the web. Don't miss the main meta tags from your code, but don't waste lines of code with pointless tags that are of no benefit to your site.