What was God doing for eternity before He created the Universe?

The Word of God reveals the answer.
John 1:1  The Word was with God.
John 1:2  The same was in the beginning with God.[In intimate, eternal fellowship]
John 17:24  Father, I will that they also, whom thou hast
                   given me, be with me where I am; that they may behold
                   my glory, which thou hast given me: for thou lovedst me 
                   before the foundation of the world.
Psalm  16:11  Thou wilt shew me the path of life: in thy presence is fulness of joy; 
                      at thy right hand there are pleasures for evermore.
Isaiah 44:6  Thus saith the LORD the King of Israel, and his redeemer the LORD of hosts;
                    I am the first, and I am the last; and beside me there is no God.

Isaiah  48:16 Come ye near unto me, hear ye this; I have not spoken in secret
                     from the beginning; from the time that it was, there am I: and now the Lord GOD,
                     and his Spirit, hath sent me.