I've started a wiki page ( How_To_Teach:_Power_Grid) for people to collaboratively develop a How To Teach Guide for Power Grid. This thread is for people to discuss, recommend or otherwise coordinate changes to be made to the guide as it is developed.
This is a bit of an experiment so I'm not sure how things will go. But if you fancy yourself a 'Game Explainer' or would like to have a guide to use while you teach the game to new users, feel free to contribute. You might want to start by discussing a change right here.