What are some common pitfalls to avoid when handling user input in PHP forms?

One common pitfall to avoid when handling user input in PHP forms is failing to sanitize input data, leaving the application vulnerable to SQL injection attacks. To prevent this, always sanitize user input using functions like `mysqli_real_escape_string()` before using it in database queries.

// Sanitize user input before using it in a database query
$user_input = mysqli_real_escape_string($conn, $_POST['user_input']);
$query = "SELECT * FROM users WHERE username='$user_input'";
$result = mysqli_query($conn, $query);