When it comes to web development, PHP frameworks play a crucial role in facilitating quicker and more efficient coding. Each framework offers unique features that cater to different project requirements, making it essential for every developer to have a solid understanding of the leading options available. Here are the top 5 PHP frameworks every developer should know:

1. Laravel - Known for its elegant syntax and robust features, Laravel has become one of the most preferred frameworks among developers. Its built-in tools for routing, authentication, and caching simplify development tasks.
2. Slim - This micro-framework is perfect for building small web applications and APIs quickly. Slim’s minimalistic approach allows developers to focus on essential features.
3. Symfony - Renowned for its flexibility and scalability, Symfony is widely used in large-scale applications. Its reusable components and extensive libraries offer a scalable solution for complex projects.
4. Yii - This high-performance framework is designed for rapid development of web applications, featuring a powerful MVC architecture that integrates easily with modern web technologies.
5. CodeIgniter - Lightweight and straightforward, CodeIgniter is ideal for beginners. It requires minimal user configuration and comes with a rich set of libraries that can be used to speed up development.

When it comes to PHP development, avoiding common mistakes is crucial for creating efficient and effective web applications. One of the common PHP development mistakes is neglecting error handling. Failing to implement proper error handling can lead to difficult debugging processes and poor user experience. It is essential to utilize try-catch blocks to manage exceptions and errors gracefully, ensuring that your application's users receive the help they need without seeing raw error messages. Additionally, not validating user input can expose your application to security vulnerabilities such as SQL injection. Always validate and sanitize input before processing it to maintain the integrity of your application.

Another frequent mistake in PHP development is the misuse of database connections. Developers often forget to close database connections, leading to resource leaks that can slow down or crash applications under heavy load. Always ensure that your database connections are closed when they are no longer needed. Furthermore, relying heavily on global variables can lead to unexpected behavior in your applications. Instead, make use of function parameters and return values to pass data around your application cleanly. By addressing these common pitfalls, developers can enhance the performance and security of their PHP applications.

Optimizing your PHP code is essential for enhancing website performance and ensuring a smooth user experience. Start by analyzing your code for any redundancies or unnecessary computations. Utilizing built-in functions instead of writing custom code can significantly improve execution speed. Additionally, caching results of expensive database queries or complex calculations can reduce server load and latency. Implement tools like OPcache to cache bytecode, which can lead to substantial increases in performance.

Another key consideration for PHP code optimization is minimizing the use of external resources. This can be achieved by decreasing the number of included files, leveraging autoloader functionality, and utilizing efficient database indices. It's also beneficial to implement error handling to avoid runtime errors that could slow down execution. By profiling your application with tools such as Xdebug, you can identify bottlenecks in your code and focus your optimization efforts where they will have the most impact.