First of all, you are in good company. Paul wrote to the Corinthians about how he felt when he first arrived among them,
I was with you in weakness and in fear and in much trembling (1 Corinthians 2:3)
The word “weakness” is the Greek word from which we get anesthesia. Paul said he felt light headed with fear. And he was trembling physically. If you’ve ever had your knees knocking--that’s how Paul felt.
So how did he do it even though scared? He tells us,
And my message and my preaching were very plain. Rather than using clever and persuasive speeches, I relied only on the power of the Holy Spirit. I did this so you would trust not in human wisdom but in the power of God. (1 Corinthians 2:4-5).
First, Paul kept it simple. He didn’t try to wow them. He knew that wouldn’t work anyway:
For since in the wisdom of God the world through its wisdom did not come to know God, God was well-pleased through the foolishness of the message preached to save those who believe. (1 Corinthians 1:21)
The gospel is not really foolish, of course. But it seems so to those who consider themselves wise in their own eyes. Dressing it up in fancy sounding words won’t change this.
Besides, it’s much easier to say something simple and plain. Don’t worry about being eloquent. Why not? Because of the second point….
Paul relied on the power of the Holy Spirit. This is the major point. Paul knew that the ability to be a witness for Christ comes directly from the Spirit, not our cleverness,
but you will receive power when the Holy Spirit has come upon you; and you shall be My witnesses both in Jerusalem, and in all Judea and Samaria, and even to the remotest part of the earth (Acts 1:8).
The result of us being weak but the Spirit being strong is that they come to trust in God’s power, not in our ability. Your responsibility is to tell people about Christ. His responsibility is to draw people to Himself. “Success in witnessing is simply taking the initiative to share Christ in the power of the Holy Spirit and leaving the results to God.”--Bill Bright.