I had a study once who would only use the Bible. I would look up all the scriptures in the jw study book and go through them as an outline. Impressed them and they did become a witness.
So just saying, have what you want to talk about written down and the scriptures to support it ready too. A lot of people are impressed with the jws ability to come up with a scripture or two to support each belief.
Keep your friend in one area of the Bible and study it in context. Otherwise, it will end up being a game of Bible hopscotch.
Good luck.