As an Internet marketing strategy, SEO considers how search engines work and what people search for. Optimizing a website primarily involves editing its content and HTML coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines.
For a search engine to recognize the value and relevance of a page, it must receive help from the creator of that page. Properly optimizing your pages to make them “search engine friendly” can greatly increase your search engine rankings, traffic levels, and potential earnings from your website.
relevancy is key along with uniqueness...don't have multiple pages have the same meta data, title/descrip/tags and your content should be indexed and ranking well in the SE's.