You have your work cut out for you, but it can be done.
It is a lot of fun, because they have a rigid indoctrination about what the Bible is about that is at such great variance with what is written that when confronted with the actual text they will start spewing all sorts of nonsensical stuff, much of it outright funny.
It is best if you don't have any doctrine that you need the Bible to prove, but are just willing to let it say what it will say.
One thing that is helpful is to avoid the proof text trap. Verses were not written in isolation, but as part of a narrative, so you only get the meaning if you read a whole chapter or more. So do that. Any verse given to you should be part of an entire chapter, This will at least diffuse the point the JW was trying to make, and will often refute the point because they carefully excise the verse they want to prove something even if that is not what it really means.
One technique is to parse your chapter and find out who is present, what are they doing and who is speaking. Graph it out. I did, and my JW saw that and often realized the Watchtower position was unworkable. Once that happens, let it go. Move on and don't make a fuss about it. They will stew on it, and you don't need to prove anything. Just say something noncommital, like "That's interesting." It's not about winning. If their mind gets guarded or closed up, you win nothing.
If your JW insists on flipping you into the "What Does the Bible Really Teach" book, then get that copy of "Response to What Does the Bible Really Teach" by Wilbur Lingle. It will help you a lot. You can let a lot of things slide by, pick and choose where you want to call out the Watchtower nonsense.
http://archive.org/details/ResponseToWhatDoesTheBibleReallyTeach
It can be a train wreck when a JW tries to explain the Bible without their Watchtower aids. See for yourself.
http://www.youtube.com/watch?v=ww75UH2Io74
