In the previous post I talked about how I see a limited number of player approaches and GM approaches that can work. I just skimmed a thread on ENworld which talks about terrible "sandbox" experiences - in short, there's either a bunch of players who are trying to play in a sandbox, but the GM is unable to provide it or the GM is providing a sandbox but the players are clueless as to how to act in it, resulting in a failed game because of mismatched expectations of how to play. So that's the compatibility problem.
You could look at that stuff and figure out what the GM is supposed to do and what the players are supposed to do so the thing comes together. Everyone at the table has a role to play - one above and beyond the usual role of a cyborg or elf or what have you. Let's call that a "job", even though the term is abhorrent in relation to gaming. So let's say there's only a few combinations of "jobs" that work. For a so-called sandbox, the GM has to do her job and the players theirs.
You can kinda see that in the "The MC, a GM" post where I tried to show that the DM's job description in an oldschool D&D game and the MC's job description in Apocalypse World were in fact very very similar. They serve different ends, with different agendas, but the hands-on stuff is almost identical. This also goes back at least to that MS Paint brainfart post almost a year ago (wow, has it really been that long).
Next post, we get down to those practices.