Philippians 4 :8-9
8And now, dear brothers and sisters, one final thing. Fix your thoughts on what is true, and honorable, and right, and pure, and lovely, and admirable. Think about things that are excellent and worthy of praise. 9Keep putting into practice all you learned and received from me—everything you heard from me and saw me doing. Then the God of peace will be with you.
When we understand the finished work of Christ and what He has done for us, there will be a copious flow of true, honourable, right, pure, lovely and admirable thoughts that will fuel our hearts with thankfullness and praises to our God.
A good start to fix our thougths on is to develop a list of all the differences between the old and the new covenant and to discover and appreciate that the new is always better than the old.