I'm hired by a company to write Accessible and W3C Valid XHTML, CSS code. although I'm very good at XHTML, CSS but want to know any tips from experts for this job? any tips related to tool, blog, book, software, process, techniques to make my work faster and better would be appreciated.
(X)HTML Validator: http://validator.w3.org/
Make Sure you use a Strict Doctype as this will make IE show everything as it should, not how IE wants it to look.
test you pages on multiple browsers, this is the best way as far as I am concerned