Have you ever convinced a religious person to become atheistic? How did you do this? How long did it take? Were the people in some sort of life crisis, or were they just living along?
This is probably a quite difficult task of persuasion. So stories how people were successful at it could be very interesting to improve ones' persuasion abilities.
Relatedly, it might be interesting to know what religious groups have gathered on techniques to convert people to their religion - are there some manuals/techniques floating around?
For convincing people in person, I've always tried to follow the maxim "Don't argue, discuss." You can present arguments, but it's important to frame them as "I think X because..." or "My take on this is X" and so forth, rather than "X is wrong because..." or "The usual solution to this is X, but that doesn't make sense because..."
With online debates, it's different because your actual interlocutor is only a small part of the audience to your arguments.