There is no point in building a website unless there are visitors coming in. A major source of traffic for most sites on the Internet is search engines like Google, Yahoo!, MSN, Altavista and so on. Hence, by designing a search engine friendly site, you will be able to rank easily in search engines and obtain more visitors.
Major search engines use programs called crawlers or robots to index websites to list on their search result pages. They follow links to a page, reads the content of the page and record it in their own database, pulling up the listing as people search for it.
If you want to make your site indexed easily, you should avoid using frames on your website. Frames will only confuse search engine robots and they might even abandon your site because of that. Moreover, frames make it difficult for users to bookmark a specific page on your site without using long, complicated scripts.
Do not present important information in Flash movies or in images. Search engine robots can only read text on your source code so if you present important words in Flash movies and images rather than textual form, your search engine ranking will be affected...