Jesus did not just send the disciples out. He told them to wait in Jerusalem until they were filled with power from above i.e. the Power of the Holy Ghost (Luke 24:49).
In Acts 1:8, we see that receiving power was a prerequisite for the disciples being witnesses for Him.
But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth. KJV
Evangelism is a spiritual activity therefore it is unwise to attempt it without the ability of the Holy Ghost. This is different from initial baptism of the Holy Ghost in the life of a believer. I am talking about being filled with the spirit.
Luke 24:53 tells us how to activate the help of the Holy Spirit in evangelism.
And were continually in the temple, praising and blessing God. Amen.
Acts 2:1 also gives us a hint of what we need to do.
And when the day of Pentecost was fully come, they were all with one accord in one place.
We know that getting men saved is God’s ultimate purpose on earth and He needs to help us get the job done. So we must allow Him.
Practically, you can allow God help you by filling up yourself with the Spirit often. This happens when you separate yourself to be alone with him in prayer, worship and study of the Word.
This is when God also works upon your heart and is able to fill you with passion for souls.
In summary, no power, no preaching!
NO POWER, NO PREACHING.