“Let the heavens praise.” In this verse, as the context reveals, “the heavens” is a metonymy for the spirit beings who dwell in heaven and who can praise God. The planets, stars, and galaxies show the glory and power of God, but they do not “praise” Him.
“assembly of the holy ones.” This seems to refer to the larger assemblies of spirit beings that God sometimes holds. God’s inner council is mentioned in Psalm 89:7 [For more on God’s divine council, see commentary on Genesis 1:26. For more on God’s presiding over a large general assembly of spirit beings, see commentary on Job 1:6].