Accessible apps

What materials, courses, tools do you know that teach how to tweak accessibility?**

  1. What do you use to learn practical stuff about tweaking it?

  2. Besides good semantics and dev tools what else do you use to improve it in your projects?

Here’s the WCAG guidelines:

Here is some article, may help you to write semantics and maintainable code

When it comes to guidelines or articles I can also add few (look at the list below).
I’m looking for some practical courses/ tutorials and free tools.