You need to know the Gospel of Jesus Christ (the good news):
You need to know your own experience:
Write out your own story (testimony) so you can be comfortable telling it to others. It is your story, not someone else’s.
You need to know your assignment:
Acts 1:8 tells us: “But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth.” Witnessing is our assignment. We don’t have to wonder what God wants us to do. We’re to be witnesses.
God didn’t say, “You shall be my lawyer.” What’s the difference between a witness and a lawyer? A lawyer argues a case; a witness tells what he has seen and heard. That’s the reason you need to know your testimony. A witness doesn’t have to know the answer to everything. All you need to know is what have you seen and what you have heard.