Tehillim: The Gates of Repentance

For the saying of Psalms has a special power for repentance. But you should occupy yourself all the year with sayings Psalms with kavvanah so as to merit coming to repentance. Likkutei Ayzot, Tshuvah, #32

According to Rabbi Weintraub Psalm 90 is good for this purpose also.

Psalms Chapter 90 תְּהִלִּים
A Prayer of Moses the man of God. Lord, Thou hast been our dwelling-place in all generations.

Before the mountains were brought forth, or ever Thou hadst formed the earth and the world, even from everlasting to everlasting, Thou art God.

Thou turnest man to contrition; and sayest: 'Return, ye children of men.'

For a thousand years in Thy sight are but as yesterday when it is past, {N}
and as a watch in the night.

Thou carriest them away as with a flood; they are as a sleep; in the morning they are like grass which groweth up.

In the morning it flourisheth, and groweth up; in the evening it is cut down, and withereth.

For we are consumed in Thine anger, and by Thy wrath are we hurried away.

Thou hast set our iniquities before Thee, our secret sins in the light of Thy countenance.

For all our days are passed away in Thy wrath; we bring our years to an end as a tale that is told.

The days of our years are threescore years and ten, or even by reason of strength fourscore years; yet is their pride but travail and vanity; {N}
for it is speedily gone, and we fly away.

Who knoweth the power of Thine anger, and Thy wrath according to the fear that is due unto Thee?

So teach us to number our days, that we may get us a heart of wisdom.

Return, O LORD; how long? And let it repent Thee concerning Thy servants.

O satisfy us in the morning with Thy mercy; that we may rejoice and be glad all our days.

Make us glad according to the days wherein Thou hast afflicted us, according to the years wherein we have seen evil.

Let Thy work appear unto Thy servants, and Thy glory upon their children.

And let the graciousness of the Lord our God be upon us; {N}
establish Thou also upon us the work of our hands; yea, the work of our hands establish Thou it.

Whomever wants to merit becoming worthy of doing tshuvah, should accustomed himself to saying psalms, for the Psalms have a special power to inspire repentance. Likkutei Aytzot, Tshuvah, #32