Any or all of the above. First I'll look at the grid fill to see if any areas can be improved. After I'm happy that the grid is as good as it can be, I'll edit the clues which can mean tweaking a few or rewriting whole swaths. Which day of the week the puzzle is scheduled for can mean making the clues easier or trickier. And when the puzzle is laid out, I might need to edit more clues to fit on the page.