Even since writing the first edition of this book from 2011 to 2012, the W3C has made strides in making it easier for authors to write more accessible web pages.
The WCAG exists to provide:
"a single shared standard for web content accessibility that meets the needs of individuals, organizations, and governments internationally."
When it comes to more pedestrian web pages (as opposed to single page web applications and the like) it makes sense to concentrate on the WCAG guidelines. They offer a number of (mostly common sense) guidelines for how to ensure your web content is accessible. Each recommendation is rated as a conformance level: A, AA, or AAA. For more on these conformance levels look at http://www.w3.org/TR/UNDERSTANDING-WCAG20/conformance.html#uc-levels-head.
You'll probably find that you are already adhering to many of the guidelines, like providing alternative text for images for example. However, you can get a brief run...