API developers should design their APIs with a focus on user experience, ensuring that they are intuitive, flexible, and easy to use. This can be achieved by following best practices such as planning and strategizing, designing for clarity and simplicity, writing code that is readable and maintainable, and providing comprehensive documentation and SDKs. Additionally, API developers should prioritize testing, versioning, authentication, limiting, throttling, consumption, documentation, SDKs, responsiveness, and scalability to ensure the success of their API. By following these guidelines, API developers can create APIs that are user-friendly, reliable, and scalable, ultimately driving adoption and success.