And while staying with them he ordered them not to depart from Jerusalem, but to wait for the promise of the Father, which, he said, “you heard from me; for John baptized with water, but you will be baptized with the Holy Spirit not many days from now.” (Acts 1:4-5)
If you feel impelled to cry to God to give you the power to preach, the spiritual power, the power of the Holy Ghost.
If you are implied to teach in the Sunday school—and it is not worth doing unless you feel that you are impelled to it and sent to it—then pray for the power to win the souls of those dear children for Christ.
If you feel called upon to write a letter to a friend tomorrow about his soul or her soul, do it because you feel called upon to do it; but pray to God to show you how to it. Pray to him to put the power into the words that you utter, that you may say the right words, and put even the right tone into those words.
There is a good deal even in the tone of the preacher. “How shall they preach, except they be sent?” (Romans 10:15 KJV). They must be clothed with divine power; but the Lord can clothe even a child with that power; he has often done it.
He can clothe a humble Christian woman, who never spoke in public, with the power to win souls; he has often done it. First tarry at Jerusalem till you are endued with power from on high; and then go forth as Christ’s witnesses; for how shall you preach, except you be sent?
 Charles Spurgeon, At the Master’s Feet [Grand Rapids: Zondervan, 2005], May 6.