There is a new fad presentation going around, a simple but loaded question. Ask the householder:
"What would it take for you to be interested in the Bible?"
Of course you can't say no, and if you say, "Nothing" the followup question is "Why?" So either you get a conversation or a door in your face.
Could we turn this around?
"What would it take for you to leave the Organisation?"
Of course a JW will usually "Nothing," but by asking "Why?" you can slide in a testing tone to the question, in effect challenging their faith. If they do answer with a specific issue, you have exposed a faultline.