UX principles are a list of timeless guidelines that inform and guide the development of a user experience. They should encapsulate the experience and be based on research findings and design ideas. Each principle should be unique, mutually exclusive, and hold true for future designs. UX principles are useful as they allow early collaboration, make it easy to communicate the experience to clients, and can be used to evaluate designs and make decisions throughout the project. Some example principles include Google Calendar being fast, visually appealing, and easy to use and share, and Microsoft Surface principles focusing on natural, seamless, social, and spatial experiences.