Once, my pastor told us that John chapters 14, 15 and 16 could be read for guidance before going to evangelize. He said these words are Jesus' final instructions to his disciples. I believed him and started reading these regularly, especially before going to evangelize.
I also had the great pleasure to teach on these chapters in a course on evangelism in my church. Under the guidance of the Holy Spirit of God, I was blessed to share the teaching. At least one new pastor has come from that class which was about 6 years ago.
As I said, God's Holy Spirit illuminated these to us in the class. I encourage you to spend time contemplating what Jesus said in these passages in order to be more effective in your evangelism.