Watch for Tweets!
On the official Destiny Twitter account, Bungie has teased that it will be giving away beta keys this week. "You might want to keep checking back in with us this week; we'll be posting #Destiny Beta codes randomly each day."
If you haven't pre-ordered Destiny yet, then this is your chance to try and get in on the beta. Just watch @DestinyTheGame on Twitter to see if you can grab a code before a billion other people try and redeem it.