What are best practices for initializing variables in PHP to avoid errors on different server environments?

When initializing variables in PHP to avoid errors on different server environments, it is best practice to check if the variable is set before using it. This helps prevent undefined variable errors that may occur if the variable is not initialized. One way to achieve this is by using the isset() function to determine if a variable is set and not null before using it in your code.

// Check if the variable is set before using it
$variable = isset($_POST['variable']) ? $_POST['variable'] : null;