Quick how-to guide..

1. Page title tag

<title>Key Search Terms</title>

The title element is the single most important on-page SEO data. Consider it carefully.

2. Keywords and description metadata tags

<meta name="keywords" content="keyword1, keyword2" />
<meta name="description" content="Key Search Terms" />

1 and 2 are key, keep the content focused and short, search engines can black-list on the basis of repetitive, long content.

3. Site verification
Submit your site via Google Web Master Tools and verify using the metadata tag technique.

<meta name="google-site-verification" content="PgmB4If5NAcmMRrSxC9Lim4VFy6bldSB2VY" />

Bing, Yahoo etc. offer similar site verification mechanisms.

4. Add a VF page called RobotsTxt (or similar)
And add content below, this page should be set as the robots.txt file in the Site config detail page.

<apex:page contentType="text/plain" showHeader="false">
User-agent: *
Allow: /
</apex:page>

The default is to block all crawler activity. The entry above provides full-access to all pages to all search engines. This can be adjusted to fit your preference – reference http://en.wikipedia.org/wiki/Robots_exclusion_standard for further detail.

Optional 5. Add the site to Google Analytics and verify by adding the tracking code to the Site via the config detail page *this adds in the necessary markup.