Robert Elmer compiled a collection of Puritan prayers with contemporary English in his excellent book, Piercing Heaven, which I highly recommend for you to add to your bookshelf. In this collection is a section with prayers in regards to giving the gospel to others. One such prayer includes the 17th Century preacher Joseph Alleine:
"O Lord, how insufficient I am for this work. With what will I piece the scales of Leviathan - or make my heart, hard as a millstone, feel what you desire it to feel?
Will I go and speak to the grave, and expect the dead to obey me and come forth?
Will I make a speech to the rocks, or lecture the mountains, and move them with arguments?
Will I make the blind see?
From the beginning of the world no one has ever heard of opening the eyes of a person born blind. But, Lord, you can pierce the heart of a sinner.
I can draw the bow at random, but you direct the arrow between the cracks of the armor.
I come in the name of the Lord of hosts, the God of the armies of Israel. I come forth, like David against Goliath, to wrestle, not with flesh and blood, but with rulers and cosmic powers, and spiritual forces of evil of this world.
This day let the Lord defeat the Philistines, take away the armor of the strong man, and give me the captives out of his hand.
Lord, choose my words. Choose my weapons for me. And when I put my hand into the bag, and take our a stone and sling it, and carry it to the mark, make it sink - not into the forehead, but into the heart of the unconverted sinner.
Take him to the ground like Saul of Tarsus.
Lord God, help! How can I leave them this way? If they will not hear me, still I pray that you will hear me. I pray that they might live in your sight! Lord, save them, or they perish.
My heart would melt to see their houses on fire when they were fast asleep in their beds. So is my soul moved within me to see them endlessly lost?
Lord, have compassion, and save them out of the burning. Put forth your divine power, and the work will be done.
Slay the sin, and save the soul of the sinner. Amen"