Here's the prayers I say before I pray the Office:
Aperi, Dómine, os meum ad benedicéndum nomen sanctum tuum: munda quoque cor meum ab ómnibus vanis, pervérsis et aliénis cogitatiónibus; intelléctum illúmina, afféctum inflámma, ut digne, atténte ac devóte hoc Offícium recitáre váleam, et exaudíri mérear ante conspéctum divínæ Majestátis tuæ. Per Christum Dóminum nostrum. Amen.
Dómine, in unióne illíus divínæ intentiónis, qua ipse in terris laudes Deo persolvísti, has tibi Horas (vel hanc tibi Horam) persólvo.
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Open, O Lord, my mouth to bless thy holy name: cleanse also my heart from all vain, evil, and foreign thoughts; illuminate my intellect, inflame my affections, that worthily, attentively, and devoutly I may be able to recite this Office, and may I be worthy to be heard before the appearance of thy divine Majesty. Through Christ our Lord. Amen.
O Lord, in union with that divine intention, by which thou thyself on earth offered thy praises to God, I offer these my Hours (or this my Hour) to you. Amen.