You'll be receiving a Halo 4 Red Avatar Suit as shown above - you may need to perform this tutorial multiple times to receive a "male" suit for your avatar as most codes you will receive are for "female" avatars. It took me a few shots to get a male avatar.
Visit the following website in "Incognito" mode in Google Chrome. You can click here or copy and paste the web address below.
Click the green button that says "Claim Coupon"
You will see some boxes where you need to enter information - please use the guide below on what to write.
Country: United Kingdom (You don't need to live in the UK, however you MUST select United Kingdom for this tutorial to work.
First Name: It can be anything you want
Email: It can be a FAKE email address
Tick the check boxes... type in the Captcha if required.
Click the "Submit" button.
You should now see an avatar code. You need to redeem this on your Xbox console or Xbox.com - If you receive a FEMALE avatar suit and your avatar is MALE, please follow the tutorial again - it may take a few tries before you receive a MALE code.
NOTE: If you wish to repeat the tutorial, close the Incognito window and open a new one.