The key principles of good GUI (Graphical User Interface) design include:

1. Clarity: Clear and concise language, intuitive icons, and simple visuals.

2. Consistency: Uniform design patterns, typography, and color schemes.

3. Intuitiveness: Logical layout, obvious controls, and minimal cognitive load.

4. Visibility: Clear and prominent display of important elements and information.

5. Affordance: Visual cues that suggest how to interact with elements.

6. Feedback: Prompt and informative responses to user actions.

7. Flexibility: Accommodating different user needs, preferences, and abilities.

8. Error prevention and recovery: Minimizing errors and providing easy recovery options.

9. Aesthetics: Visually appealing and engaging design.

10. Usability testing: Validating design decisions through user testing and feedback.

By following these principles, GUI designers can create interfaces that are easy to use, efficient, and enjoyable, ultimately enhancing the overall user experience.