Immediate UX actions I've taken in my designs to ensure accessibility:

• Make sure your text's contrast is 100% compliant to AA standards. For example, this sentence wouldn't pass. It's hard to see. You can use tools such as Stark directly in your design work to speed up the workflow.
• Include percentages in data legends near any data visualization. For example, if you just use colors to represent data, how would a colorblind person be able to distinguish? An example would be "Unregistered Users (22%).
• Don't use spatial copy like "see below" since the page can be responsive and text shifts can cause confusion.
• Form a relationship with your company's legal department to catch any WCAG discrepancies. For example, there may be a dedicated WCAG legal expert on hand to help.
• Make sure your company's IT department, specifically where your developers are, know about WCAG and the back-end work that needs to be done. This can be how screen-readers and other devices interact with your digital products. Additionally, compliance sheriffs do exist to catch these discrepancies.
  
• You can check out this awesome Invision article about inclusive design!

You can read about the four main ideas, as explained by UX Planet:

​Principle One — Perceivable
Information and user interface components must be presentable to users in ways they can perceive.
​This principle addresses the fundamentals of information and content presentation, such as compositional sequence, colors, contrasts, contextual relationships and display of text, among others.

Principle Two — Operable
User interface components and navigation must be operable.
This principle addresses such elements as navigation, headings and labels, keyboard-only navigation and ways of preventing unwanted physical reactions to the content, such as seizures.

Principle Three — Understandable
Information and the operation of user interface must be understandable.
This principle looks at the user’s ability to understand the content, namely the structure and style of the language. It also addresses a number of interactive considerations, such as on-focus and on-input, as well as navigation patterns.

Principle Four — Robust
Content must be robust enough that it can be interpreted by a wide variety of user agents, including assistive technologies.
This principle addresses a number of technical considerations of the content presented via assistive technologies.