Search Engine Optimization is a collection of strategies that improve the level at which your web site is ranked in the result returned when a user searches for a key word or phrase.
SEO is maost sucessful when you concentrate on one effort at a time. A great place to start concentrating is on the way your web site is built. One of the first thing that attracts a Search Engine Crawler is the actual design of your site. Tags, Links, Navigational Structure and content are just a few of the elements that catch crawlers's attention.

Types of Search Engine

There are several types of Search Engine. Beyond the primary , Secondary & Targeted Search Engine. There are given bellow.

Primary Search Engine

A primary search engine is the type you think of most often when search engines come to mind. Some index most or all sites on the Web. For example, Yahoo! Google, and MSN are primary (also called major) search engines. Primary search engines will generate the majority of the traffic to your web site, and as such will be the rimary focus of your SEO efforts. Each primary search engine differs slightly from the others.
Most primary search engines are also more than just search. Additional features such as e-mail, mapping,news, and different types of entertainment applications are also available from most of the primary search engine companies. These elements were added long after the search was established, as a way to draw more and more people to the search engine. Although those features don’t change the way people search, they might affect which search engine people choose.

Secondary Search Engine

Secondary search engines are targeted at smaller, more specific audiences, although the search engine’s content itself is still general. They don’t generate as much traffic as the primary search engines, but they’re useful for regional and more narrowly focused searches. Eg. of secondary search engines includeLycos, LookSmart, Miva, Ask.com, and Espotting. econdary search engines, just like the primary ones, will vary in the way they rank search results. Some will rely more heavily upon keywords, whereas others will rely on reciprocal links. Still others might rely on criteria such as meta tags or some proprietary criteria.
Secondary search engines should be included in any SEO plan. Though these search engines might not generate as much traffic as the primary search engines, they will still generate valuable traffic that should not be overlooked. Many users of secondary search engines are users because they have some loyalty to that specific search engine. For example, many past AOL users who have moved on to broadband Internet service providers still use the AOL search engine whenever possible, because it’s comfortable for them.

Targeted Search Engine

Targeted search engines — sometimes called topical search engines — are the most specific of them all. These search engines are very narrowly focused, usually to a general topic, like medicine or branches of science, travel, sports, or some other topic. Examples of targeted search engines include CitySearch, Yahoo! Travel, and MusicSearch, and like other types of search engines, ranking criteria will vary from
one to another.
When considering targeted search engines for SEO purposes, keep in mind that many of these search engines are much more narrowly focused than primary or secondary search engines. Look for the targeted search engines that are relevant to your specific topic (like pets, sports, locations, and so on).