According to the World Wide Web Consortium (WC3):
The WC3's Web Accessibility Initiative provides a wealth of information on making web content accessible to everyone. Helpful starting points include:
Another helpful resource is WebAIM's Introduction to Web Accessibility, which includes information on implementing web accessibility and principles of accessible design. WebAIM also provides many services, articles, resources, and discussion forums.
In this brief video from WebAIM, students share some of their experiences with the web and accessibility: