Prayer Before Reciting Sefer Tehillim

Yehi ratzon milfaneicha A-do-nai eloheinu ve'elohei avoteinu, habbocher bedavid avdo uvezar'o acharav, vehabbocher beshirot vetishbachot, shettefen berachamim el keri'at mizmorei tehillim she'ekra, ke'ilu omaram david hamelech alav hashalom be'atzmo, zechuto yagen aleinu. Veya'amod lanu zechut pesukei tehillim uzechut tevoteihem ve'otiyoteihem unekudoteihem veta'ameihem, veA-do-naiot hayotze'im mehem merashei tevot umisofei tevot, lechapper chatoteinu va'avonoteinu ufesha'einu, ulezamer aritzim velehachrit kol hachochim vehakotzim hasovevim et hashoshanah ha'elyonah, ulechabber eshet ne'urim im dodah be'ahavah ve'achavah vere'ut. Umisham yimashech lanu shefa lenefesh ruach uneshamah letaharenu me'avonoteinu velisloach chatoteinu ulechapper pesha'einu, kemo shesalachta ledavid she'amar mizmorim elu lefaneicha, kmo shene'emar. Gam A-do-nai he'evir chatatecha lo tamut. Ve'al tikachenu meha'olam hazeh kodem zemanenu, venizkeh lechayim arukim tovim umetukanim, be'ofan shenuchal letaken et asher shichatnu. Uzechut david hamelech alav hashalom, yagen aleinu uva'adenu sheta'arich appecha ad shuvenu elaicha bitshuvah shelemah lefaneicha. Ume'otzar matnat chinam chanenu kedichtiv. Vechanoti et asher achon verichamti et asher arachem. Ucheshem she'anu omerim lefaneicha shirah ba'olam hazeh, kach nizkeh lomar lefaneich A-do-nai eloheinu shir ushevachah la'olam habba. Ve'al yedei amirat tehilim tit'orer chavatzelet hasharon, velashir bekol na'im begilat veranen, kevod halvanon nitan lah, hod vehadar beveit eloheinu, bimherah beyameinu, amen selah.

Lechu nerannenah layeya nari'ah letzur yish'enu.
Nekaddemah fanav betodah bizmirot naria lo.
Ki el gadol A-do-nai umelech gadol al kol elohim.

Prayer before Tehillim on a Weekday

May it be the will before You, Hashem, our G-d, and the G-d of our forefathers, Who chose David His servant and his offspring after him, and Who chose songs and praises - that you attend with mercy to the recitation of psalms that I shall merit and consider it as if they were recited by King David, of blessed memory, himself, may his merit be a shield over us. And stand in our favor may the merit of the verses of the psalms together with the merit of their words and their letters and their vowels and their cantilations, and together with the Holy Names that are formed from them, from the initial (letters) of the words and from the final (letters) of the words - may their merit serve to bring atonement for our transgressions, iniquities, and sins, and to cut down ruthless men, and slash away all the thorns and briars which surround the Rose, Celestial; and to unite the Bride of Youth with her Beloved in love, brotherhood, and companionship. And from that (unification) may be drawn to us an abundant blessing to our spirit, breath and soul, to purify us of our iniquities, to forgive our sins and to atone for our transgressions, just as You forgave David who recited these very same psalms before You - as it is said: Hashem also has forgiven your sin, you shall not die. May you not take us from This World before our time, until the completion of our years, (among them are seventy years,) in a manner that we be able to rectify anything that we have ruined. May the merit of King David, of blessed memory, shield over us and for us; that You may be patient (with us), (and wait) until we return to You in repentance that is complete before You. From your treasury of grace that is undeserved, be gracious to us - as it is written: I am Compassionate to those whom I favor, and I am Merciful to those upon whom I have mercy. And just as we recite before You a song in This World, so let us merit to recite before You - O Hashem, our G-d - songs and praises in the World to Come. And through the recitation of the psalms arouse the Rose of Sharon to sing with a voice that is pleasant, with ecstasy and joy. May the glory of the Levanon be given to her, majesty and splendor in the House of our G-d, speedily in our days. Amein. Selah!

Before Saying Tehillim it is customary to say these Three Verses

Come! Let us sing joyfully to Hashem, let us call out to the Rock of our Salvation,
Let us greet Him with thanksgiving, with praiseful songs let us call out to Him.
For a great G-d is Hashem, and a great King above all heavenly powers.