What I tell people in session 0 who have never played L5R:
-Creation myth.(Just basics, but I do go over the Sun and the Moon and the Kami)
-Celestial Order(to me this is very important, it drives home their place in society)
-Bushido
-The clans and their place in society(i.e. What they do. Crab defend the wall, Lion fight wars for the Emperor, Crane run court, etc)
-Swords and sword etiquette(don't draw it unless you intend to use it, how you hand it over, what wearing one means, etc)
-Honor and what it means
My guidelines for first time players:
-Never give them real power in the society.
-Always, always, always... remind them what their actions mean in society. If they continue, their fault. I do this for 4-5 sessions, after that they should get it and are on their own.
-I never let a new player play a Scorpion. I've been playing this game for over 15 years and I still don't think I can play a Scorpion well. I think there are very few people who actually can.
-Put them into a social situation asap. So they know the pitfalls.
-Put them into a combat asap. So they know the ramifications.
-Do whatever it takes to drive home that this is NOT D&D.