@Lisse24 @Ninjakitten While I'm not Sao or Roz, I do staff with them and was part of these conversations. Some of the things that surprised me that were a real problem for players are perfectly obvious things, in retrospect, like 'page' and 'look' -- and also what an @alias actually is. Is it an IC nickname? What? Terms like GM, TP, all of these words that are just part of our common lexicon leave new players going '???'.
The 'look' thing in particular jars me. I've used channel spawns for so many years that it never occurred to me just how many players were struggling with the fact that the instructions in the welcome room were getting scrolled right off the screen by the volume of the cheerful chatter on the Newbie channel.
Channels -- what they are, how they work, if they are IC / OOC -- are also a thing that gets to them. It seems to make sense to them when I talk about channels as chat rooms, and that you can be in multiple chat rooms with one account at the same time, but then trying to figure out how to explain to them that game is set up as a series of rooms, which is totally different than the chat room channels, that you navigate through by using exits never sounds as intuitive as it could be.
We do a lot of explaining to people just how to even connect and how to talk, on channels and in rooms: say, pose, emit, etc. People trying to connect and being greeted by white text on a black screen has apparently been incredibly intimidating for a good number of our players.
http://lostandfound.riverdark.net/wiki/Cheat_Sheet is the cheat sheet that was put together by one of our new-to-MUing staffers, who checked in with a couple of our other brand-new-to-MUing players. That's more of a list of commands that people who are already pretty well hooked need to look up than it is an onboarding list, though. Others have already said it, but the absolute best thing you can really do for onboarding is having people communicating with new players, and have a friendly, patient welcome crew. We're lucky in that we have an exceptional group of players for that.