how should i start to build an apple watch app

To start building an Apple Watch app, you can leverage the existing work you've done for iOS, especially if you've already implemented live activities. Here are some steps and considerations based on the content from WWDC:

1. Leverage Existing iOS Live Activities: If you have live activities on iOS, these can automatically appear on the Apple Watch in the smart stack. This is a great starting point as it allows you to reuse your existing code and design.

2. Use Xcode Previews: Utilize the all variants preview in Xcode to see how your live activity will appear on watchOS. This helps in visualizing and customizing the user interface for the Apple Watch.

3. Customize for Apple Watch: Consider adding a custom watchOS presentation by supporting the small supplemental activity family. This allows you to tailor the experience specifically for the Apple Watch, making it more timely, contextual, and functional.

4. Explore New APIs: With watchOS 11, there are expanded capabilities for widgets and live activities. You can enhance your app by integrating these new features to provide a richer user experience.

5. Check Out Relevant Sessions: For more detailed guidance, you can refer to sessions like "Bring your Live Activity to Apple Watch" and "Design Live Activities for Apple Watch" from WWDC 2024.

For a more detailed walkthrough on customizing live activities for Apple Watch, you can check the session Bring your Live Activity to Apple Watch (03:22).