What are some best practices for including files in PHP projects?

When including files in PHP projects, it is best practice to use the `require_once` or `include_once` functions to prevent multiple inclusions of the same file, which can cause errors. Additionally, it is recommended to use absolute paths for including files to ensure that the correct file is included regardless of the current working directory.

// Example of including a file using require_once with an absolute path
require_once __DIR__ . '/path/to/file.php';