Knowing HTML/XHTML well definitely gives you an edge in website development. After checking with the checklist below, you can move on to the design and CSS sections.
For HTML,
Know how to start your own website
Know about tags and their uses
Know about empty elements and nesting of elements
Know the use of attributes in elements
Have some knowledge on DTD (explore deeper item)
For XHTML,
Know what XHTML is
Know the importance of XHTML for your website
Know how to convert your HTML document into XHTML
Able to validate your website
Take a short quiz on HTML/XHTML
