I think the WM should know the ritual, the bylaws, and how to run a meeting. That said I agree with the other posts that a lot of lodges don't have this luxury,
but on the other hand if the WM has gone thru the chairs -- he is supposed to be able to do the EA degree as JW, the FC as SW and the MM as WM, this should mean he knows the ritual.
I know one brother who indicated to me that he had been WM of his lodge for 14 consecutive years
(talk about recycling) and this year he had decided not to take the East again and feels great. That particular lodge had raised 2, 3 or 4 brothers every year but they suspended 4 or 5 every year for NPD. This year they have raised 6 and suspended 0.