This one may seem obvious to some, especially those who already carry it with them.  I assert that carrying a song in your heart is a key to happiness.  Music has the ability to reinforce our mood or change it.  A song can buoy us in times of great pain, or comfort us in times of sorrow.  With music we can express our deepest feelings and desires.  When we sing with our heart, the song that resides within us becomes our song, our expression.

Putting a song in our heart, enables us to  worship that which we desire to serve.  So choosing the right song(s) to carry us through life is paramount as we search for joy that can bring us happiness.  Will the joy we find be temporary (worldly), or everlasting (heavenly)?

Shout with joy before the Lord, O earth!  Obey him gladly; come before him, singing with joy.  Try to realize what this means–the Lord is God!  He made us–We are his people, the sheep of his pasture.  Go through his open gates with great thanksgiving; enter his courts with praise.  Give thanks to him and bless his name.  For the Lord is always good.  He is always loving and kind, and his faithfulness goes on and on to each succeeding generation.  Psalm 100 NLT

Now that is something worthy to sing about!  May the song in your heart offer praise to the God who created you, His Son, Jesus, who saved you, and His Spirit equipped to guide you all the days of your life.