Sing every day - Even if one has reviewed his learning, he should sing it every day, and this will cause your life in the World to Come to be with happiness and songs.
The Mystical Power of Music by Avraham Aryeh Trugman (pg.41) - "The word for "song" in Hebrew is shirah, equaling 515, the same as the word for prayer, tefillah. This is not a mere casual connection, but rather a fundamental lesson on the essence of prayer and song.
Then Moses sang- Then when he saw the miracle, it rose in his heart that he should sing a song.
(כג) וְהָיָה בִּהְיוֹת רוּחַ אֱלֹקִים אֶל שָׁאוּל וְלָקַח דָּוִד אֶת הַכִּנּוֹר וְנִגֵּן בְּיָדוֹ וְרָוַח לְשָׁאוּל וְטוֹב לוֹ וְסָרָה מֵעָלָיו רוּחַ הָרָעָה.
(23) And it came to pass, when the [evil] spirit from God was upon Saul, that David took the harp, and played with his hand; so Saul found relief, and it was well with him, and the evil spirit departed from him.
(19) Now therefore write ye this song for you, and teach thou it the children of Israel; put it in their mouths, that this song may be a witness for Me against the children of Israel.