The best way to help a JW leave their religion, is to understand them. They honestly believe they have the truth and you are wrong. They are blind but sincerely believe they are living in spiritual paradise. They will not listen to anything you have to say because they read their Bible more than most Christians. The problem is they look to their religion to tell them what the Bible means. No matter what the Bible actually says, they do not understand it the way you understand it. They understand it based on what people in authority tell them is the truth.
One of the best ways to understand the Witnesses is to read every article on this website. The more you read, the more you'll understand how cults operate. It's fascinating how the human mind can be controlled and manipulated without any realization that this is happening.
The following videos are extremely helpful as well. Listen to them several times. If you approach a Jehovah's Witness in the right way, you can accomplish much. If you use the wrong approach (and most people do), you will fail every single time.