Don’t think of anything special here, refer a friend promotions are really simple. You can buy a coupon for your friend and if that person registers for the photo book editor, creates a first book and orders it (for a certain minimum price), you will get a discount. A similar, yet less “painful” way, is if you send an email to the friend, he goes through the registration and ordering process, and in the end both you and your friend will receive a coupon.