i think you have to mostly just go with where the Spirit leads you, where the conversation leads. sometimes, you just need to start with whatever they might be asking questions about Now, there's something really important to know. The word witness means "someone who tells their story." Before someone can know what God can do for them or anything else, you need to tell them what God has done for you. At some point in your life, God has delivered you from something or other. Start with your story. No one knows it better than you, and it can sometimes be the most powerful witnessing tool. You also need to start by establishing God's existence and also by telling Jesus' story. Those are the things you need to establish before you can actually get into any type of theology with them. Sin is also something that is very important to get to. No one can repent if they dont recognize that they need forgiveness.