What are some best practices for organizing and including PHP files to prevent class redeclaration errors?

Class redeclaration errors can be prevented by using PHP's `include_once` or `require_once` functions to include files that contain class definitions. This ensures that a class is only declared once, preventing redeclaration errors. Additionally, organizing your PHP files into separate directories based on functionality can help prevent naming conflicts and make it easier to manage and include files.

// Include the file containing the class definition using require_once
require_once 'path/to/your/class/file.php';

// Instantiate the class
$classInstance = new ClassName();