Today's #1 most important search engine is probably Google. Google relies on an idea of link popularity or "PageRank" to determine the ranking of results. The current dominance of this type of ranking system greatly diminishes the value of many traditional (and much abused) methods of getting near the top of a search listing. The official information on this technology is pretty slim. More interesting is the inside scoop on Google's PigeonRank.
Of course, in order to get anywhere on any search engine your page also has to establish relevance to a particular search, for this all the old rules still apply pretty well.
In general, shooting for specific terms to be easily found under is better than using general terms. While maintaining a natural style, keywords and key phrases should be used early in the content.
After years of misuse and abuse abuse <META> tags are often ignored by the big public search engines altogether. They can still have use in internal search mechanisms but in all cases <META> tag keywords should be under 1,000 characters including spaces with NO repetition. <META> tag descriptions will be displayed in many search engines to entice surfers to visit your site and should be under 200 characters in length including spaces.<META> tags like <TITLE> tags should be in the <HEAD> section of your page.
Watch out for frames. Frames may confuse search engines even more than they confuse some users. Redirects, JavaScript and DHTML can also interfere with indexing.
Investing in your domain name pays off for any public facing site. Over-registered, free and low cost domains are often ignored by the search engines.
It can take six weeks or more for you to show up in some of the major search engines. Furthermore, the full impact of any changes are often not felt for six months or more.