Heeding the God of Truth (2 Timothy 3:16,17)

As we profess to be Christians we are called to live our lives for our Lord as living sacrifices.  Our catechism summarizes this so well when it states that we live our lives out of gratitude for our Lord because He has redeemed us.  So, how do we learn what living for the Lord looks like?  How do we know if we are living for the Lord?