Key principles of user experience design include usability, accessibility, and user-centered design. Focusing on usability ensures that products are intuitive and efficient for users to navigate, while accessibility guarantees that all individuals, regardless of ability, can use the product. A user-centered approach emphasizes understanding user needs and incorporating their feedback throughout the design process. Other principles include consistency in design elements and visual hierarchy to guide user attention effectively. By adhering to these principles, designers create engaging, effective, and satisfying experiences for users.