To complete the Emperor's Decree quest you will need to:
1) Like our Facebook page
2) Invite 2 friends in the game
3) Tag a friend who invited you
You will be able to complete the second quest objective after two of your friends tag you as an inviter.
To tag the inviter open the Emperor's Decree quest window and hit the Tag button. You will be able to choose a person in the list and tag them.
If you don't want to tag anyone, hit the Skip button under the list. Note: this cannot be undone!