IMO and I have been shot down here before for giving the same answer, but here it goes
the first step is for every adherent of every denomination within the Christian world to study their own faith, to read the bible in the spirit with which it was written (which is to say, without an agenda), to obey the commandments, and to order their own lives to holiness and continuing conversion, and most of all love, love for God, love for Jesus, love for their co-religionists, love for friends, love for enemies. If the love comes first, unity will inevitably follow, because love cannot abide division.