To pray a psalm, read it slowly and aloud if you can, saying the words as your own prayer rather than studying them as a passage; when a line stops you, stay there until it has been prayed. The rest is knowing which psalm to open, what to do with verses that do not fit you, and staying long enough for the book to teach you its language.
The church's oldest prayer book
The Psalter has been the working prayer book of Jews and then of Christians for well over two thousand years, because it is the part of Scripture written to be said back. The Mishnah, compiled around 200 CE, records the Levites singing an appointed psalm in the Temple for each day of the week. The cry Matthew and Mark record from the cross is the opening line of Psalm 22, "My God, my God, why hast thou forsaken me?" — a psalm that goes on, "why art thou so far from helping me, and from the words of my roaring?" Athanasius, writing to Marcellinus in the fourth century, named what is peculiar about it: elsewhere Scripture is another man's speech; the psalms the reader takes on his own lips as though he had written them.
Their origins are less settled than the headings suggest: the superscription rendered "of David" uses a preposition meaning by, for, or belonging to, and the dating of individual psalms is contested. Greek and Latin Bibles number one behind the Hebrew, so Augustine's exposition of Psalm 137 is filed under 136.
How the traditions move through it
The great traditions did not pray the Psalter by picking favorites, though they never agreed on how to move through it. Benedict's Rule assigns the whole book across a single week. The Byzantine churches divide it into twenty kathismata, also a week, and twice a week through Great Lent. Cranmer's Book of Common Prayer spreads it over a month, about five psalms a day at morning and evening prayer, with Psalm 119 broken across three days; later Anglican books revised that. Rome's Liturgy of the Hours has used a four-week cycle since the 1971 reform.
The variety is the point; what they agree on is the cycle — you receive the psalm the day hands you, not one that flatters your mood. Begin smaller than a monastery: one psalm morning and night carries you through the book in about two and a half months.
The psalms that curse
Sooner or later the cycle hands you Psalm 137, which begins with exiles weeping by the rivers of Babylon and ends: "Happy shall he be, that taketh and dasheth thy little ones against the stones." Psalm 139 turns from the tenderest lines in the book to "I hate them with perfect hatred: I count them mine enemies." Psalm 109 asks that a man's days be few and another take his office.
Serious readers have handled these three ways, and the traditions never converged. Some omit them: the Roman four-week psalter drops Psalms 58, 83, and 109 entirely, and verses elsewhere, citing a psychological difficulty — though the older Roman breviary kept them, and Anglican and Orthodox psalters keep them still. Some read them figuratively, as Augustine did, taking Babylon's infants for evil desires still small enough to be dashed, and the rock for Christ. Some pray them as they stand, on the ground that the psalm is the alternative to vengeance, not its rehearsal. Bonhoeffer, writing in 1940, argued they can be prayed only as Christ's prayer — a reading still contested, since that same Christ asks from the cross that his enemies be forgiven.
The church never deleted them: Peter, in Acts, applies Psalm 109 to Judas. What you must not do is pretend the verses are not on the page.
Whose words are you saying?
There are two ways to hold a psalm. One is to say it as your own speech, meaning every word. The other is to read it overheard rather than claimed — what an honest person does with "For I have kept the ways of the LORD, and have not wickedly departed from my God" on a day he plainly has not.
If you can say it, say it. If you cannot, say it for someone to whom it is true today; the book is prayed by more people than you. Praying a lament you do not feel is not dishonest; it is stocking words for the week you will have none.
Where to begin
For grief, Psalm 6 gives permission to be undone: "I am weary with my groaning; all the night make I my bed to swim; I water my couch with my tears." Then Psalm 88, which every consoling instinct wants to fix, ends: "Lover and friend hast thou put far from me, and mine acquaintance into darkness." Prayer is allowed not to resolve.
For gratitude, Psalm 103 turns you toward your own soul: "Bless the LORD, O my soul, and forget not all his benefits." Psalm 116 asks the harder follow-up: "What shall I render unto the LORD for all his benefits toward me?"
For fear, Psalm 56 has the least sentimental line in Scripture: "What time I am afraid, I will trust in thee." Not if. Psalm 27 answers its own question: "The LORD is my light and my salvation; whom shall I fear?"
For sleeplessness, Psalm 4 is the old night prayer: "I will both lay me down in peace, and sleep: for thou, LORD, only makest me dwell in safety." Psalm 121 says the thing worth hearing at three in the morning: "he that keepeth Israel shall neither slumber nor sleep."
If it helps to have the cycle kept for you, Seraph has a free reading plan through the Psalms, no account required, and the complete King James Bible bundled in the iPhone app. But nothing here needs an app: a Bible, a chair, and a psalm a day will do it, and has, for a very long time.