To handle form validation errors in a GUI:

1. Display errors clearly: Show errors in a prominent location, using clear language.

2. Error messaging: Provide specific, concise error messages.

3. Highlight errors: Visually highlight fields with errors.

4. Real-time validation: Validate fields as users type.

5. Prevent form submission: Block submission until errors are fixed.

6. Focus on error fields: Automatically focus on the first field with an error.

7. Error summaries: Provide a summary of all errors at the top.

8. Inline validation: Validate fields inline, rather than on submission.

9. User-friendly language: Use non-technical language for error messages.

10. Accessibility: Ensure error messages are accessible for all users.

11. Error recovery: Allow users to easily recover from errors.

12. Feedback mechanisms: Provide feedback for successful form submission.

By following these guidelines, you can handle form validation errors in a way that is user-friendly, clear, and helpful, improving the overall user experience.