When a person is convinced that they are trying to save your soul, no tactic is off the table. The possible outcomes are either the greatest possible reward or the greatest possible penalty. If they must take unorthodox -or even underhanded- steps to get you to the reward, it is worth it.
In other words, the indoctrinator must be indoctrinated first. Makes him a very effective recruiter.
Once someone is in, indoctrination takes the simple form of the one thing that proves most effective at shaping our behavior: repetition. Second to that is fear. Cults will endlessly do two things: keep you busy in study and repetition, and making sure you are afraid of straying from that path. The WT publications and videos are not shy about constantly repeating how important it is to be obedient, how close the end is, and what happens to those who are on the wrong side of God's justice at the end (and they can get quite graphic with those descriptions!).
Always read the publications. Always attend the meetings. Always go out in field service. Spend any available time in those pursuits. If you stop to enjoy life for a moment, make sure you are with your brothers in the faith (preferably, those who are upstanding members of the congregation). Do not stray from this path. If you have any questions or doubts, read the publications and/or speak with an elder. Do not seek out answers on your own from any other source.
It's not just that you isolate yourself from non-believing people. You also isolate your mind from non-believing thoughts. Until I realized I was an atheist and therefore not a JW, I was terrified of even thinking about finding non-JW information, much less seeking out anti-JW information. That is indoctrination.