I've been crewing as part of a particular LARP system for a while now. The roles I play are almost invariably handed to me. I'll frequently have a short brief and 5 minutes of prep before it's showtime and I need to go out and actually play this character, delivering some plot to the players and giving them another part of our universe to interact with.
We've a modestly-sized pool of crew to draw from, given our number of players. We get people who have never LARPed before joining all the time. Sometimes, though, the players ask a character a question, and the crew member just clams up. The referee who's running the encounter - usually a more confident and experienced LARPer - has to "fish" them, feeding lines into their ear and letting the character deliver them. This kind of sucks for both the players and the crew. I understand why it happens, I've needed fishing before, too, but I feel far more confident now and I've no idea what changed to make this happen.
Now that I am a more confident and experienced LARPer myself, I'm expected to take out groups of fresh LARPers, brief them, and be their referee. At this point, it's my responsibility to make their characters as easy and natural to play as possible.
What can do I do make this easy for them?
Should I aim to flesh out their characters for them, or let them pick details they feel comfortable with?
Should I steer them away from certain roles? What kind?
Does being thrown in the deep end help, or should I be easing people in slowly?
I expect that the right answer to this is "it depends on the person", but when dealing with someone I've only just met and who may well already be a bit nervous, what sorts of questions are constructive to ask them, and what can generally help people feel more comfortable?