The World Wide Web Consortium (W3C) have issued a draft "Easy Checks - A First Review of Web Accessibility" for comment. The document is intended to help assess the accessibility of a web page. However it uses concepts which a non-expert will not be familiar with. It is unlikely that many people will have the patience to study this document. Instead I suggest encouraging the use of automated checkers, which give the user a quick automated check, explain how to do additional manual checks and provide links to detailed information.
Those wanting more detailed understanding should be encouraged to undertake a training course on web accessibility. This could be one of the free on-line courses available, or one at a vocational training institution.
I talked about my experience
assessing the Sydney 2000 Olympic website and providing some advice for the Beijing 2008 Olympics.