This has probably been brought up before but I believe that creating a "refer a friend" referral link program would be the best and most lucrative way for Steemit to gain popularity.
Think about all the Facebook friends or Youtube subscribers who would be much more inclined to join the site when you can send them a personal link for them to join with a free (2-5 SBD) for the two of you just for signing up! I think doing so would greatly increase the value of Steem and its popularity will grow exponentially.
Let me know what you think in the comments :)