What best practices can be followed to improve the security and functionality of PHP scripts?

One best practice to improve the security and functionality of PHP scripts is to sanitize user input to prevent SQL injection and cross-site scripting attacks. This can be done by using functions like htmlentities() or mysqli_real_escape_string() to escape special characters before inserting them into a database or displaying them on a webpage.

// Sanitize user input to prevent SQL injection
$user_input = $_POST['user_input'];
$clean_input = mysqli_real_escape_string($connection, $user_input);

// Display sanitized input
echo htmlentities($clean_input);