The W3C has laid down 4 principles of web accessibility. 1. Perceivable - Users must perceive the information and user interface components easily. For example, you can have alt text for the images that describe what the image is about. 2. Operable - The website and UI components must be operable. People must be able to navigate your website using both the mouse and keyboard. 3. Understandable - The content and UI operations must be understandable. They have to make sense by writing specific error messages. 4. Robust - Your content must be robust enough for a wide array of assistive technologies used by the disabled to interact with your website.