In November 2008 Google published - almost unnoticed by the target audience - a first version of his Search Engine Optimization Starter Guide. This 22 page document, in PDF format, seems to me like the ideal beginner’s guide. It’s perfect for site managers who don’t follow all the latest tech news but who need to demystify all the fuss that is made around SEO.
It informs, in plain English, about best practices to apply to get your site ranked higher in search results. We are basically following these rules when creating new sites. I think that this is excellent reading for clients who want to have a better understanding about type and amount of work that is done when we do "SEO".
You can download the document here
Good place to get started with SEO: the Google Webmaster Central Blog
You may also go to the blog post of the Google Webmaster Central Blog if you want to read the document in another language. At the time of publishing this post was also available in Chinese, German, Portuguese, Spanish and Turkish.
By the way: if you want to dig deeper, have a look at the complete Webmaster Central Blog