As a Ruby developer, leveraging the right gems can significantly enhance your productivity and streamline your projects. Here are 5 essential gems every Ruby developer should know:

1. Rails - This full-stack framework is the backbone of most Ruby applications, providing a comprehensive set of conventions and tools.
2. Devise - A flexible authentication solution for Rails applications that makes implementing user authentication easy.
3. RSpec - A powerful testing tool that allows developers to write readable tests for their applications, ensuring code quality and reliability.

Continuing with our list, the following gems provide critical functionalities that can make your development process smoother:

4. Capybara - An integration testing tool that simulates how a user would interact with your application, making it easier to test web applications.
5. Pry - An alternative to the standard IRB shell that offers advanced features and better debugging capabilities.

By integrating these essential gems into your workflow, you can enhance your development efficiency and create robust applications.

Optimizing your Ruby on Rails application for performance is crucial to ensure a smooth user experience and efficient resource management. Start by examining your database queries. Use tools like the bullet gem to identify and eliminate N+1 queries which can degrade performance. Additionally, consider implementing eager loading to fetch related records more efficiently. It's also vital to configure caching mechanisms properly; using fragment caching and page caching helps reduce response times by serving stored content instead of recalculating it each time a page is accessed.

Another standout practice is to minimize asset loading by compressing your JavaScript and CSS files using the webpacker gem. This ensures that your application loads faster by reducing the amount of data transferred over the network. Additionally, leverage the Rails environment settings to serve static assets, which can dramatically improve response times. Lastly, consider employing background jobs with tools like Sidekiq for processing time-consuming tasks, preventing your application from becoming sluggish and allowing it to focus on handling user requests efficiently.

Ruby development, while powerful and flexible, is not without its common pitfalls that can hinder project success. One major issue developers encounter is poor performance. Ruby, being an interpreted language, can sometimes lead to slower applications, especially when using inefficient code. To avoid this, it's crucial to optimize code by utilizing built-in methods and minimizing object allocation. Additionally, employing tools like the Ruby Benchmark module can help identify bottlenecks and improve overall performance.

Another frequent pitfall is lack of proper testing. In the fast-paced world of development, it's easy to overlook rigorous testing, which can lead to bugs in production. Developers should adopt a culture of test-driven development (TDD) to ensure that code is tested before it goes live. Utilizing testing frameworks such as RSpec or MiniTest can significantly enhance the reliability of code and help avoid many common issues.