Not a lot. It depends. I come up with a setting and basic premise. If the players don’t like it, then we negotiate a bit. If it doesn’t fly, it doesn’t happen. I file the idea away and move on to the next one. If it clicks with the players, at least enough to start, we go from there: sometimes it is modified a bit depending on what the players say, and how the character generation session goes. That can evolve the world concept quite a bit, but it’s an organic process done with the players, so that can add a lot of player ideas into the world.

Then we start play. If it ‘clicks’ then we’re good. If not, it folds, generally by mutual agreement. If it ‘clicks’, then I go with the flow, and that can then see significant changes in the setting/premise. Not always, but sometimes. Games evolve.