Use semantic markup that provides a meaningful structure to the document (i.e. web page)
Semantic markup also refers to semantically organizing the web page structure and publishing web services description accordingly so that they can be recognized by other web services on different web pages. Standards for semantic web are set by IEEE
Use a valid markup language that conforms to a published DTD or Schema
Provide text equivalents for any non-text components (e.g. images, multimedia)
Use hyperlinks that make sense when read out of context. (e.g. avoid "Click Here.")
Don't use frames
Use CSS rather than HTML tables for layout.