Below are the top 10 ranking factors I believe that not just Google but other search engines use as part of their organic search results ranking algorithm:

  1. Keyword use in title tag
  2. Keyword use in domain
  3. Keyword use in body text (the first 100 words are more important)
  4. Anchor text of inbound link
  5. Age of site
  6. Link popularity within the site’s internal link structure
  7. Number of inbound links
  8. Relevance of inbound links
  9. Popularity of linking sites
  10. Speed of your site (this is new and is confirmed by Google’s top engineer Matt Curtis that this will be considered as early as 2010)

Any webmaster designing a new website or a website-owner optimizing an existing site should at least consider the top 10 SEO factors listed above.