This might be totally common knowledge, but I learned about it in passing, from a Fallout video last night, and as far as I know, it hasn't been mentioned here yet:

If you visit Bungie Rewards (https://bungie.net/rewards/), the top item on the page is a free Prime Engram. Just for being part of the rewards program (which I thought was pretty close to automatic, anyway).

Go get it. Because who doesn't like free?