Here are some prayers of preparation for Mass, from Appendix I of the Sacramentary (pp. 1006-1009).
Prayer of St. Ambrose
Lord Jesus Christ,
I approach your banquet table
in fear and trembling,
for I am a sinner,
and dare not rely on my own worth
but only on your goodness and mercy.
I am defiled by many sins
in body and soul,
and by my unguarded thoughts and words.
Gracious God of majesty and awe,
I seek your protection,
I look for your healing;
Poor troubled sinner that I am,
I appeal to you, the fountain of all mercy.
I cannot bear your judgment,
but I trust in your salvation.
Lord, I show my wounds to you.
I know my sins are many and great,
and they fill me with fear,
but I hope in your mercies,
for they cannot be numbered.
Lord Jesus Christ, eternal King, God and man,
crucified for mankind,
look upon me with mercy and hear my prayer,
for I trust in you.
Have mercy on me,
full of sorrow and sin,
for the depth of your compassion never ends.
Praise to you, saving sacrifice,
offered on the wood of the cross for me
and for all mankind.
Praise to the noble and precious blood,
flowing from the wounds of my crucified
Lord Jesus Christ
and washing away the sins of the whole world.
Remember, Lord, your creature,
whom you have redeemed with your blood.
I repent my sins,
and I long to put right what I have done.
Merciful Father, take away
all my offenses and sins;
purify me in body and soul,
and make me worthy to taste the holy of holies.
May your body and blood,
which I intend to receive,
although I am unworthy,
be for me the remission of my sins,
the washing away of my guilt,
the end of my evil thoughts,
and the rebirth of my better instincts.
May it incite me to do the works pleasing to you
and profitable to my health in body and soul,
and be a firm defense
against the wiles of my enemies. Amen.
Prayer of St. Thomas Aquinas
Almighty and ever-living God,
I approach the sacrament of your only-begotten Son, our Lord Jesus Christ.
I come sick to the Doctor of Life,
unclean to the Fountain of Mercy,
blind to the Radiance of Eternal Light,
and poor and needy to the Lord of Heaven and Earth.
Lord, in your great generosity,
heal my sickness, wash away my defilement,
enlighten my blindness, enrich my poverty,
and clothe my nakedness.
May I receive the bread of angels,
the King of kings and the Lord of lords,
with humble reverence,
with the purity and faith,
the repentance and love,
and the determined purpose
that will help to bring me salvation.
May I receive the Lord’s body and blood,
and its reality and power.
may I receive the Body of your only begotten Son, our Lord Jesus Christ,
born from the womb of the Virgin Mary,
and so be received into His Mystical Body
and numbered among his members.
as on my earthly pilgrimage
I now receive your beloved Son
under the veil of a sacrament,
may I one day see Him face to face in glory,
who lives and reigns with you forever. Amen.
Prayer to the Virgin Mary
Mother of mercy and love,
blessed Virgin Mary,
I am a poor and unworthy sinner,
and I turn to you in confidence and love.
You stood by your Son
as he hung dying on the cross.
Stand also by me, a poor sinner,
and by all the priests
who are offering Mass today
here and throughout the entire Church.
Help us to offer a perfect and acceptable sacrifice
in the sight of the holy and undivided Trinity,
our most high God. Amen.
Statement of Intention (for Priests)
My purpose is to celebrate Mass
and to make present the body and blood of our Lord Jesus Christ
according to the rite of the holy Roman Church
to the praise of our all-powerful God
and all his assembly in the glory of heaven,
for my good
and the good of all his pilgrim Church on earth,
and for all who have asked me to pray for them
in general and in particular,
and for the good of the holy Roman Church.
May the almighty and merciful Lord
grant us joy and peace,
amendment of life,
room for true repentance,
the grace and comfort of the Holy Spirit,
and perseverance in good works. Amen.