A Lancaster University Resource for Students and Staff 
Use the right doctype - article by Eric Meyer:
www.oreillynet.com/pub/a/network/2000/04/14/doctype/index.html
Straightforward introductions to web standards can be found at:
http://www.w3.org/Consortium/Points/
http://www.w3.org/QA/2002/04/Web-Quality
Details of the specifications (for advanced HTMLers only):
There are a number of websites that offer comprehensive summaries of deprecated code:
http://www.internet-tips.net/html/depreciated.htm
The 2 links below are from W3C HTML specification and indicated which elements and attributes have been deprecated:
Index of elements
http://www.w3.org/TR/REC-html40/index/elements.html
Deprecated attributes
http://www.w3.org/TR/REC-html40/index/attributes.html
Visit Eric Meyer's (CSS Guru) web site:
CSS Properties summary:
http://www.pageresource.com/dhtml/cssprops.htm
Browser compatability chart: