In most cases a Search Engine Spider will grab only the first few words, sentences or paragraphs of a web page, and use those words as the description and keywords for your Web page. META Tags on the other hand tell the Spider what information to use.  

Meta Tags contain descriptive attributes of a web page and can be used to help categorize the contents of a web page.  Some Search Engines will use the information found in Meta Tags to help categorize your web pages.  

Theoretically, we could all create the appropriate Meta Tag information for each of our web pages and the search engines could "spider" these to categorize all of the web pages on the internet.   But that would be too easy...

Because search engine placement is so important to being found in the sea of web pages that exist in a single category, many web masters have been overly creative in specifying the content of their Meta Tags in an attempt to enhance that placement.  

A Search Engine loses its benefit if it cannot identify web sites that are relevant to the search terms entered, so the Search Engine developers have had to become just as creative in identifying truly relevant sites.  That means that they have had to look further than just the Meta Tags, and into the actual content of your web pages to determine relevance.  They all have their own proprietary algorithms, but generally they still start with the Meta Tags, compare the information found in the Keywords Tag to the Title Tag, the Description Tag, and some portion of the actual text inside the Body Tag.  The similarities/differences in these various portions of the web page are weighted and ranked, resulting in one or more relevance factors that are then used to determine placement of a page in relation to other pages that meet a given search criteria.

All pretty complex, huh?  Well, it gets worse!  The Search Engine developers are constantly refining their algorithms, becoming more sophisticated in determining relevance, and in identifying blatant attempts to subvert their algorithms.  What's a body to do?

A simple, honest approach is best.  Don't try to cheat the algorithms.  If you are new enough to all of this that you didn't already know everything I've said so far - then you are also new enough to all of this that you will fail miserably if you try to cheat the system.

Start by defining and organizing your web pages around the content you intend to provide - without a single thought to Search Engine Placement.  Then actually create the content (web pages).  Again, with no consideration given to Search Engine Placement.  It doesn't matter how good you are at getting placement if the content is not going to be 

1. relevant, and 
2. of value. 

At some point, you will decide on a Title for each page.  (HINT - If you outlined your entire web site like a term paper first, then your outline contains each page title.)  The Title of the web page will, of course, reflect the content of that page, and should be included in the Title Tag.  The Title Tag is free form, and contains the exact title of the web page, so it is the easiest (takes less thought) tag to create.

Part of this process is to create META Tags. You may have trouble figuring out what to put in your META Tags. Which keywords do I use? Use words that fit the contents of your site. Say you created a site about Sam Jones. Sam likes surfing, volleyball and hot dogs. Use ‘Sam Jones‘ in your title, description and in your list of key words. If you do that then your site will be more heavily weighted on Sam Jones and less on surfing, volleyball and hot dogs. The search engines will search the contents of your page to see if you indeed talk about Sam Jones.

To achieve a high position in the search engines it is best to concentrate on a small number of words and include them in the title, description and keyword META tags as well as at the start of your web page. As more keywords are added, the relevance of each is diluted resulting in a lower score by some search engine algorithms.

Avoid the temptation to stuff too many words in your META tags and avoid repeating your keywords as this may be considered spamming by some engines resulting in your site being blacklisted, penalized or banned.

Some search engines concentrate on only the <TITLE> tag and very little else.  Some search engines ignore the META tags altogether and concentrate on the body of the web site.

Remember no matter what you do to optimize your page for one engine today may not take the same page to the top spot in another search engine, or even the same search engine in the future.  So if you‘re not willing to spend your full time keeping up with the changing search engine technology then just keep it simple and honest and the search engines will eventually find a way to find you.  After all their goal is to find the most relevant sites for a given search.

One technique that works well for search engines is to check a site's popularity.  What do we mean by popularity?  It‘s not actually how many times the site is visited.  After all the search engines themselves are sending users to the pages. They judge the popularity of a site by how many links exist to your site. The theory is that if a human checked out your site and thought it was worthy enough to put an actual link to it then it must have some content of value.  So this again leads us to conclude that your site must have value.

Another type of ‘Search Engine‘ which is not really a search engine at all is a human edit directory.  How much would you be willing to bet that the search engines check out these human edited directories to add weight to sites listed in them?  These are a great place to get your site listed.  Remember at the heart of Yahoo lies the granddaddy of all human edited directories.