Parallelism is common in Hebrew poetry. (See: [[rc://en/ta/man/translate/writing-poetry]] and [[rc://en/ta/man/translate/figs-parallelism]])
The psalmist is speaking to all of God's people, so you should use the plural command form if your language has one. (See: [[rc://en/ta/man/translate/figs-pronouns]])
# a new song
Possible meanings are 1) "a song you have never sung before" or 2) a song no one has ever sung before.