When it comes to enhancing your Ruby on Rails application, incorporating the right gems can make all the difference in terms of functionality and performance. Here are five essential gems that every Rails developer should consider:

1. Devise: A flexible authentication solution that streamlines user registration and session management.
2. Pundit: A lightweight authorization library that helps manage user permissions effectively.
3. ActiveAdmin: An easy-to-use framework for creating elegant backends for your application.
4. Sidekiq: A powerful background job processor that enables the handling of asynchronous tasks seamlessly.
5. Rubocop: A static code analyzer that helps maintain a clean and consistent codebase by enforcing style guidelines.

Integrating these gems not only boosts your application's capabilities but also enhances maintainability and user experience. For instance, with Devise, your authentication process becomes robust and highly customizable, while Pundit ensures that users have the right access to different parts of your application. Utilizing ActiveAdmin can significantly reduce the time spent on building admin panels, allowing you to focus on features that matter most. In addition, having a tool like Sidekiq enables your app to perform tasks in the background, improving responsiveness, while Rubocop maintains quality standards by catching potential issues early in the development process.

Optimizing your Rails application for performance is crucial to ensure a seamless user experience and efficient resource management. Start by analyzing the performance bottlenecks in your application using tools like New Relic or Skylight. These tools can help you identify issues such as slow database queries and rendering times. Once you've pinpointed the problem areas, consider implementing techniques like caching, which can drastically improve response times. You can use built-in Rails caching mechanisms, such as fragment caching and Russian doll caching, to optimize your views and minimize unnecessary database calls.

Another effective way to enhance the performance of your Rails application is by optimizing Active Record queries. Ensure you are eager loading associations using includes to avoid N+1 query problems. Additionally, employ database indexing on frequently queried fields to accelerate lookups. Another tip is to offload time-consuming tasks to background jobs using libraries like Sidekiq or Delayed Job. This not only enhances performance but also keeps your application responsive, especially during peak traffic times. By following these strategies, you can significantly boost the performance of your Rails application.

When developing applications with Ruby on Rails, one of the common pitfalls is not adhering to the DRY (Don't Repeat Yourself) principle. This can lead to code duplication, making your application harder to maintain and scale. Developers often fall into the trap of writing similar code across different controllers, which can be avoided by utilizing concerns or service objects. Another frequent issue is neglecting to write adequate tests, which can result in introducing bugs during future modifications. It is crucial to cultivate a habit of writing unit tests and integration tests to catch errors early in the development cycle.

Another major pitfall is over-complicating the application architecture. Many developers aim to implement too many features at once, which can lead to an unwieldy codebase. To avoid this, it's essential to focus on agile development practices by iteratively building the application and continuously seeking feedback. Further, undervaluing the importance of performance optimization is a mistake that can affect user experience. Developers should regularly profile their applications using tools such as Bullet or New Relic to identify bottlenecks and optimize query performance. Always remember that quality and maintainability should take precedence over merely adding functionalities.