Two Meta tags that are important are KEYWORDS and DESCRIPTION. You have to be very careful about how these are developed and positioned. Frequency and location of the keyword that is being searched are important criteria that determine relevance and hence page ranking. The search engine would generally consider the page more relevant if the keyword that is being sought is in the TITLE tag or is in the KEYWORDS tag near the top of the page. Similarly if the sought after keyword is found being repeated in the page, it may give the impression that this is a more relevant page and improve ranking.
There is a caveat, though. The above is only a general rule that has been often followed by many search engines, but then there are many variants to it. Several players in the SEO industry have tried to proclaim that this is the gospel truth and hence it has spawned a large number of experts that suggest and resort to keyword stuffing and spamming (repeating long strings of keywords). The result can often be just the opposite. Some search engines penalize pages that have keyword spamming. Some will just ignore these pages. Some engines also do not read Meta tags. The intelligent method today is to stay away from spamming and to use tags judiciously. Blend your technique to attain the right frequency and location, but stay away from any excess or spamming.
You can provide an in-depth list of words and phrases in the KEYWORD Meta tag. These words should have some relevance to the specific page or, at least, to your website. While you can vary the case of the keywords, you'll want to concentrate on the lower case because over 90% of the searches either use lower case or are conducted on search engines that are not case sensitive.
These keywords should contain variations on the same theme. If your site was about gardening, you could use garden, gardening, home and garden, home gardening, vegetable garden, and herb garden. These are all words that might be used in searches for information that your site might provide. The keywords Meta tag is not intended to replace the actual text on your website. This tag is simply to aid the spider in collecting accurate information about your web pages.
The DESCRIPTION tag is used by search engines like Inktomi for the page summary that is displayed on the results page. This summary is what the visitor will read and decide whether he/she wishes to enter your site. If the description is just full of repeated keywords, it won't do you any good, even if your page is ranked high. You still do not have a visitor. May be you have put off a visitor.
Meta Robots Tag
This is probably the only other prominent Meta tag. This is a very peculiar tag in the sense that it indicates what web pages should not be indexed by Search Engines. The Robots tag is inserted in between the header tags. An example of the Robots Tag is given below:
<TITLE>This page should be kept out of Search Engine listings</TITLE>
<META NAME="ROBOTS" CONTENT="NOINDEX">
By default, a crawler will try to index all your web pages and will try to follow links from one page to another. This can be prevented by using the Robots Tag. Most major search engines support the Meta robots tag. The Meta robots tag also has some extensions offered by particular search engines to prevent indexing of multimedia content.
There are other Meta. tags apart from the ones explored above but most of them are simply ignored by almost all search engines.
To sum up, some search engines will give you a boost if you have Meta tags. But don't expect that to necessarily be enough to put you in the top ten. Meta tags are mainly a design element you can tap into, a crutch for helping information-poor pages better be acknowledged by the search engines.
While Meta tags are not the complete answer to the question of "How do I improve my search engine ranking?" they can help with some search engines. Since there are millions of pages with Meta tags, you can add all the pages you want and still not control a sizeable percentage of the pages on the World Wide Web.
They are information inserted into the "head" area of your web pages. Other than the title tag, information in the head area of your web pages is not seen by those viewing your pages in browsers. Instead, Meta information in this area is used to communicate information that a human visitor may not be concerned with. Meta tags, for example, can tell a browser what "character set" to use or whether a web page has self-rated itself in terms of adult content.
Meta tags may help you with some search engines, so you'll want to consider adding them to every page you create. On the other hand, you can find many highly ranked web pages without Meta tags. For example, Meta tags have no effect on how humans will view your pages and enter your information into directories like Yahoo.