Cynthia Ng and Michael Schofield have published "A Practical Starter Guide on Developing Accessible Websites" in the Code4Lib Journal.
Here's an excerpt:
There is growing concern about the accessibility of the online content and services provided by libraries and public institutions. While many articles cover legislation, general benefits, and common opportunities to improve web accessibility on the surface (e.g., alt tags), few articles discuss web accessibility in more depth, and when they do, they are typically not specific to library web services. This article is meant to fill in this vacuum and will provide practical best practices and code.