Angular is a powerful front-end framework that provides a plethora of features to enhance web application development. As a developer, mastering the following five features can significantly improve your productivity and the performance of your applications: 1. Two-Way Data Binding: This feature allows automatic synchronization of data between the model and the view, simplifying the management of dynamic content. 2. Dependency Injection: Angular's built-in dependency injection system facilitates better organization by reducing the need for tightly-coupled code, making your applications more modular and easier to test.

Beyond the essential features mentioned, understanding 3. Components and Templates is vital, as they are the core building blocks of any Angular application. Each component encapsulates its own functionality, making your code more reusable and maintainable. 4. Observables and Reactive Programming with RxJS is another crucial aspect, allowing you to handle asynchronous data streams effectively. Finally, 5. Routing and Navigation in Angular enables the creation of single-page applications with seamless transitions, improving user experience by managing app states without refreshing the entire page.

Building responsive web applications with Angular requires an understanding of its core features and best practices. First, ensure that you have a solid grasp of Angular's component-based architecture. This involves creating reusable components that can adapt to different screen sizes. To start, you should utilize Angular’s built-in tools like the ngClass and ngStyle directives, which allow you to conditionally apply CSS classes and styles based on the current device or screen resolution.

Furthermore, employing Angular Flex Layout can significantly enhance your web application's responsiveness. This library provides a powerful API for layout design and allows you to create complex responsive layouts using a set of directives. To maintain consistent styling, use media queries along with Angular's responsive utilities. Lastly, testing your application on various devices and utilizing browser developer tools can help ensure that the UI scales effectively, providing a seamless user experience across all platforms.

Angular development is powerful, but like any framework, it comes with its own set of challenges. One of the common pitfalls developers face is failing to understand the component lifecycle. This can lead to issues such as memory leaks or inefficient rendering. For instance, if developers do not properly use lifecycle hooks like ngOnInit and ngDestroy, they may inadvertently retain references to resources that should be released. To avoid this pitfall, it’s essential to have a solid grasp of Angular's lifecycle and ensure that resources are cleaned up efficiently.

Another frequent mistake in Angular development is the misuse of services and state management. Often, developers create too many services or fail to share them appropriately across components, leading to data inconsistency and increased complexity. To prevent this, it is crucial to adopt a clear service architecture and utilize Angular's RxJS for reactive programming, enabling better data flow and management. By consolidating state management and maintaining a predictable data flow, developers can create more maintainable and scalable applications.