When it comes to web development with Ruby on Rails, leveraging the right tools can exponentially enhance your productivity. Below, we showcase the Top 5 Rails Gems that not only streamline your development process but also improve application performance. These gems are designed to simplify common tasks, allowing developers to focus on building innovative web applications.

1. Devise - An essential gem for managing user authentication, Devise provides a flexible authentication solution that simplifies user management.
2. CanCanCan - This authorization library allows developers to easily manage user permissions, ensuring that security is a top priority.
3. ActiveAdmin - For those needing an efficient admin interface, ActiveAdmin offers a robust framework that saves time on backend development.
4. Sidekiq - A background processing tool that utilizes Redis to manage background jobs seamlessly, Sidekiq helps enhance application performance by allowing time-consuming tasks to be processed asynchronously.
5. RSpec - This testing framework encourages behavior-driven development, making it easier to write and maintain tests for Rails applications.

Building a scalable web application with Ruby on Rails involves a combination of strategic planning and optimized coding practices. First, it's essential to define the architecture of your application. Utilize the Model-View-Controller (MVC) framework that Rails offers, which separates your application's logic, data, and user interface. Additionally, implement RESTful routing to manage your resources efficiently. Remember that the key to scalability is to be proactive; leverage background job processing with tools like Sidekiq or Delayed Job for tasks that don't require immediate user feedback.

Next, focus on database optimization and caching techniques. Use Active Record queries wisely to minimize database load, and consider integrating a caching layer with tools such as Redis or Memcached. This will significantly enhance your application's performance under high traffic conditions. Don't forget to monitor performance using tools like New Relic or Skylight to identify bottlenecks. By following these steps, you can ensure that your Ruby on Rails application remains responsive and scalable, even as your user base grows.

When embarking on your journey to learn Ruby on Rails, it's essential to avoid common pitfalls that can hinder your progress. One frequent mistake is skipping the fundamentals of Ruby before diving into Rails. Rails is a framework that builds upon the Ruby programming language, so understanding its syntax, object-oriented principles, and data structures is crucial. Without a strong foundation in Ruby, you may find it challenging to grasp Rails concepts. Tip: Consider dedicating time to master Ruby basics before tackling Rails.

Another mistake to steer clear of is neglecting to familiarize yourself with the Rails conventions and community practices. Rails emphasizes convention over configuration, meaning it has established ways of doing things that can greatly enhance your productivity once you understand them. Ignoring these conventions can lead to writing inefficient and convoluted code. To prevent this, take the time to read the Rails Guides and engage with the Rails community through forums and social media. This approach will not only save you time but also help you write cleaner, more maintainable code.