1. robots
2. content-type
3. description
4. keywords
Sequencing of these tags may be extremely important. I say “may” because SEO is mostly hypothesis due to the changing algorithms of the search engines. Even though the W3C states that tag attributes do not have to be in any particular sequence, I’ve noticed a significant difference when I have the tags and attributes in the order described here. The only deviation from the list above is that the Title tag should come after content-type and before description.
http://all-seo-tip.blogspot.com/search/label/Top%2010%20SEO%20tips