What are some common pitfalls to avoid when modifying PHP scripts for website customization?

One common pitfall to avoid when modifying PHP scripts for website customization is not properly sanitizing user input, which can lead to security vulnerabilities such as SQL injection or cross-site scripting attacks. To solve this issue, always sanitize and validate user input before using it in your scripts.

// Example of sanitizing user input using the filter_var function
$user_input = $_POST['user_input'];
$clean_input = filter_var($user_input, FILTER_SANITIZE_STRING);