Ultimately, God will show you what that specific person needs in order to be saved. One thing believers often forget is the authority they have in this world. We become intimidated by numbers of people, or flows of conversations. It is amazing how easy we forget that the God of the universe lives inside of us. Don't lose grip of the fact that you, plus God, equals the majority.
Prayer is extremely important also.
Never doubt what God can do. Pray for the lost. The Word of God is also a powerful tool in witnessing. No tricks to it, just read off some verses out loud. You'll be empowered by them.