"Sing to him a new song; Do YOUR best at playing on the strings along with joyful shouting" (NWT 1984).
"Sing unto him a new song; play skilfully with a loud noise" (KJV).
Play skillfully with a loud noise - literally, "Do well to play;" or, "do well in playing." That is, do the work well, or with all the skill of music. The word rendered "loud noise," means properly "a shout of joy" or "rejoicing:" Job 8:21; 1 Samuel 4:5. It is especially applied to the sound or clangor of trumpets: Leviticus 25:9; Leviticus 23:24; Numbers 29:1. There is rather the idea of "rejoicing" than of "noise" in the word. The meaning is that the music should be such as would be expressive of the highest joy.
JFB mentions 1 Samuel 16:17.
John Trapp's Commentary:
Play skilfully (or lustily) with a loud noise] Make good music, set all your skill and might at work to magnify the Lord. It is not an easy matter to praise God aright; it must be done Corde, ore, opere, with the very best of the best. Benefacite canendo, cum iubilatione.
Coffman's Commentaries on the Bible:
"Play skillfully with a loud noise" (Psalms 33:3). Some modern translators love to inject instrumental music into as many passages of the Old Testament as possible; and, in keeping with that intention, the RSV renders this place, "Play skillfully on the strings, with loud shouts." "The words on the strings are not in the Hebrew text." The words were simply added to the sacred text by the translators!
NET Bible: Sing to him a new song! 2 Play skillfully as you shout out your praises to him! 3
Notes from NET:
2 sn A new song is appropriate because the Lord is constantly intervening in the lives of his people in fresh and exciting ways.
3 tn Heb “play skillfully with a loud shout.”