Cleaning up PHP Code
<p>I've noticed I am a very sloppy coder and do things out of the ordinary.</p>

<p>Can you take a look at my code and give me some tips on how to code more efficiently? What can I do to improve?</p>

<pre><code>session_start();



/*check if the token is correct*/
if ($_SESSION['token'] == $_GET['custom1']){

    /*connect to db*/
    mysql_connect('localhost','x','x') or die(mysql_error());
    mysql_select_db('x');



    /*get data*/

    $orderid = mysql_real_escape_string($_GET['order_id']);
    $amount = mysql_real_escape_string($_GET['amount']);
    $product = mysql_real_escape_string($_GET['product1Name']);
    $cc = mysql_real_escape_string($_GET['Credit_Card_Number']);
    $length = strlen($cc);
    $last = 4;
    $start = $length - $last;
    $last4 = substr($cc, $start, $last);
    $ipaddress = mysql_real_escape_string($_GET['ipAddress']);
    $accountid = $_SESSION['user_id'];
    $credits = mysql_real_escape_string($_GET['custom3']);




    /*insert history into db*/
    mysql_query("INSERT into billinghistory (orderid, price, description, credits, last4, orderip, accountid) VALUES ('$orderid', '$amount', '$product', '$credits', '$last4', '$ipaddress', '$accountid')"); 
    /*add the credits to the users account*/
    mysql_query("UPDATE accounts SET credits = credits + $credits WHERE user_id = '$accountid'");

    /*redirect is successful*/
    header("location: index.php?x=1");
}else{

    /*something messed up*/
    header("location: error.php");
}
</code></pre>
