Started taking Introduction to Accessibility by W3C (https://www.edx.org/course/web-accessibility-introduction), and I'm learning a bunch! The instructors have disabilities themselves, so I like that I get to see them use assistive technologies while teaching.
I'm also reading the excellent Accessibility for Everyone book (https://abookapart.com/products/accessibility-for-everyone) from @laura. It's been helpful for me to see markup and code examples to understand things better.
@jagtalon's personal instance