What are the best strategies for managing state in complex React.js applications?

For more complex React.js applications, consider using state management libraries like Redux or Context API for global state management. Namely, Redux offers a centralized store for state, making it easier to manage and debug, and its Context API is suitable for lighter applications and avoids prop drilling. Also, consider breaking down your application into smaller, manageable components, each with its own local state. Use hooks like `useState` and `useReducer` for local state management. For asynchronous operations, on the other hand, `useEffect` is useful for managing side effects.