This is a beautiful prayer before Mass written by St. Ambrose:
“I draw near to the table, of Your most delectable banquet
dear Lord Jesus Christ.
A sinner, I trust not in my own merit; but, in fear and trembling,
I rely on Your mercy and goodness. I have a heart and body marked by my grave offensives,
and mind and a tongue I have not guarded well.
For this reason, God of loving kindness and awesome majesty,
I, a sinner caught by many snares, seek safe refuge in You.
For You are the fountain of mercy.
I would fear to draw near to You as my judge, but I seek You out as my Savior.
Lord, I show You my wounds, and I let You see my shame.
Knowing my sins are many and great, I have reason to fear.
But I trust in Your mercies, for they are beyond all numbering.
Look upon me with mercy, for I trust in You, my Lord Jesus Christ, eternal
king, God and man,
You who were crucified for mankind.
Have mercy upon me, You who never cease to make the fountain to Your mercy flow,
for I am full of sorrows and sins. I praise You, the saving Victim offered on the
wood of the cross for me and for all mankind.
I praise the noble Blood that flows from the wounds of my Lord Jesus Christ,
the precious Blood that washes away the sins of all the world.
Remember, Lord, Your creature, whom You have redeemed with Your own Blood.
I am sorry that I have sinned, and I long to put right what I have done.
Most kind Father, take away all my offenses and sins, so that, purified in body and soul,
I may be made worthy to taste the Holy of Holies.
And grant that this holy meal of Your Body and Blood, which I intend to take,
although I am unworthy, may bring forgiveness of my sins and wash away all my guilt.
May it mean the end of my evil thoughts and the rebirth of my better longings.
May it lead me securely to live in ways that please You, and may it be a strong protection
for body and soul, against the plots of all my enemies.