from reddit:
"Want to check out the strategy guide for Destiny? Just head to
http://www.primagames.com/code and use the following code (create an account on the website first):
hmnr-nqd9-d8u8-ftav
Oddly enough, it seems that the code can be used unlimited times. Doesn't seem to matter what store you say you got it from, and for the date I entered 09/08/14."
also
Once you're logged in, go to your profile, click Codes, and click Use Now next to each code to activate them and redeem them for the cards.