Mike Davidson tried to rank for the term lodefizzle on Google. He wrote a dozen different pages to find out what aspects of HTML Google really cares about. Scroll down to the Google…

  1. The H1 tag does indeed assert some dominance and we can therefore assume you are better off using proper headings in your HTML documents.
  2. The mere appearance of many nested tables in your code does not have a strong enough negative effect to be considered a drag on search engine ranking.
  3. It’s not clear that validity helps search engine ranking, but it’s definitely true that certain errors in your code can get you completely removed from indexes.
  4. The semantic effect of hierarchical HTML headings is a stronger factor in search rankings than more rudimentary measures such as physical keyword placement.
  5. Although good semantics are somewhat valuable in optimization, simple things like proper titles, descriptive filenames, and incoming links are dramatically more important.