Meta data provides information about a site. In the past this information gave search engines an idea of what a site is about. Since meta data is hidden away in a site's markup, visitors can't see it, but the search engines did. There are several types of meta data, but for the sake of this document will only be addressing three: meta keywords, meta descriptions, and the title tag.
Being hidden, lead to webmasters abusing them, which in term meant that these elements lost their high relevance and today have little, to no importance when determining the ranking of a page on the major search engines.
There was a time (pre 2000) when the TITLE, Description and Keywords were the top three primary factors in search engine ranking.
Today, based on Google's claim of looking at more than 200 factors in determining the quality of a document, they give the TITLE 3.00 points, Description 1.00 point, Keywords 0.25.
In first place we have Google, the top search engine (75%) stating that the META data won't impact your ranking in the search results.
The significant players that make up the balance are Yahoo, Bing, Windows Live and Ask who do however state that both the META Description Tag and META Keywords Tags will help in your rankings.
While it is undisputed that Google is the most popular search engine in the world, there is an argument that says that it's a bad idea to not put meta keywords in a site's markup:
However with respect to South African users, it has been a long time since I have heard utterances of search engines other than Google.
Search engines are engineered to find information that visitors want. This means the best way to make your website accessible is to design it for humans. Your website must be easy to navigate and filled with the information that they are looking for. If you can accomplish this, then the search engines will inevitably find you.
Every page in your website should include a title with a description of what that page is about. A total of 60 characters work best. The title tag should contain some of your keywords. It is important to remember this tells the search engines what your site is about, and it is also used as the link that shows up in the search results on Google, so use a compelling title that gives users a clear reason to click on it.
All images on your website should have "alt" tags or alternative text. "Alt" tags are used to describe the image when the server can not find the image for which it is looking. Also, Google will look to see that you have added the "alt" tags in your images so that vison impaired visitors will still have access to your content. Google will rank your site higher for keeping it accessible to people with disabilities. Another side benefit is that "alt" tags can increase your keyword density.
Use a few different keywords and keyword phrases that describe what your website is about. Use these and other related keywords, but only when it is natural to do so. Be careful not to over-do your keyword density or this could be viewed as spamming by Google. A good rule of thumb is to write the content like you are writing for human beings and not for search engines. For best optimization results use them in headings, links and the general copy of the website.
Users searching the web aren’t searching for design and graphics. They are searching for content. If your site does not have the content for which users are searching, then no one will look at it. Or if they do, they won’t stay very long.
This is the most important page of your website and the key to your site being found in the search engines. Your home pages should easily summarize the rest of your website and be easy to understand. Studies have shown that you have about 10 seconds to grab the users attention and keep them on your site. Your home page should have keywords in the title, heading, first few sentences of the first paragraph if possible, and alt tags in images on the home page. You should also continue to use keywords in the rest of the content on the home page whenever it is natural to do so.
Search engines pay much attention to the links on your site and the words that you use in them. The more relevant the links on your page, the more "findable" your website will become in the search results.