The Book of Psalms ends with six psalms of praise. Psalm 150 is the last of these, the last in the book, and so helps us reflect on the entire book, all of the songs the ancient people sang and that we still--well, not sing so much--use to guide the words we use to address God.
This psalm begins and ends with the word Hallelujah--The NRSV translates if for us, praise God.
Psalm 150 gives directions for us in praising God. It tells us where, why, how, and who.
Where: in church and everywhere else, as well.
Why: in recognition of what God has done and can do.
How: with trumpet, lute, harp, tambourine, dance, strings, pipe, cymbals (I'm assuming the organ in the church can substitute for all these except for dance--what are we going to do about the dance part? maybe the organist would agree to help out with this as well?)
Who: everybody who breathes
[Under the heading "Quibbles with Commentaries" I read verse 1 as directing us to praise the Lord wherever we are, both in the sanctuary and out of it. The New Interpreter's Study Bible, on the other hand, reads this verse to mean that God's sanctuary is not in the earthly temple but in the heavens.]