Etihad are currently running a nominate and earn promotion. This promotion rewards existing members for signing new members up to the frequent flyer programme.
All you need to do is become a member of the Etihad frequent flyer programme and fly with them before the 31st December. As a reward you will earn up to triple the usual amount of miles for this first flight.
If you are intending to take a flight with Etihad before the 31st December and are NOT a member of their frequent flyer programme send me a pvt message and I can refer you.