Sing unto him - Sing before him; offer him praise.
Sing psalms unto him - The word here rendered "sing psalms" means properly "to prune," and then, to" cut off," as a discourse at regular periods; or, to utter in rhythmical numbers; and then it means to accompany such words with an instrument of music. The idea here is, that he is to be approached, not merely with "singing," but with sentiments expressed in the form of regular composition - in musical numbers.
Talk ye - The word used here very commonly means to meditate, to muse (compare the notes at Psalm 1:2), but would here seem to be employed in the sense of "talking over," to wit, in singing. That is, In the psalms used let there be a "narrative" of what God has done. Let his works be the subject of the words used in the psalm.
Of all his wondrous works - Of what he has done that is suited to excite wonder and admiration. Compare Psalm 77:12.

Talk ye of all his wondrous works - נפלאתיו niphleothaiv, "of his miracles." Who have so many of these to boast of as Christians! Christianity is a tissue of miracles; and every part of the work of grace on the soul is a miracle. Genuine Christian converts may talk of miracles from morning to night; and they should talk of them, and recommend to others their miracle-working God and Savior.

Sing unto him, sing psalms unto him,.... Both vocally and instrumentally, with the voice and upon instruments of music, as were used in David's time. Psalm, hymns, and spiritual songs, are to be sung now, even the song of Moses, and of the Lamb. The wondrous things God had done for his people were sufficient matter for a song; and these were to be put into one, to be transmitted to posterity: it was usual in ancient times to hand down the history of memorable events by a song.
Talk ye of all his wondrous works: all the works of the Lord are wonderful; what David elsewhere says of himself may be said of them, that they are wonderfully made, even the least and most inconsiderable of them; and especially his works of grace, when it is observed for whom they are performed, or on whom they are wrought; sinful creatures, enemies to God, and deserving of his wrath. These are to be talked of freely and frequently, in friendly conversation, in order to gain a further knowledge of them, and warm each others hearts with them, and to lead into adoring and admiring views of the love and grace of God in them; and all of them deserve notice, none should be omitted, all are worthy of consideration and contemplation; for so the words may be rendered, "mediate" (z) "on all his wondrous works" Here is a large field for meditation; and when the heart is in a proper frame for it, meditation on the works of God is sweet, pleasant, and profitable.
(z) "meditamini", Cocceius, Gejerus, Michaelis.