Sometimes you get an idea that overarches the story, or a large portion of it. Then the problem is elaborating it down to sufficient detail to work. Like -- here the queen has trouble with rebellious nobles, and then you have to define why they rebel, and how, and what makes them dangerous without letting them overthrow the queen at once and send the story veering off in the wrong direction.
Sometimes you get small, bright ideas that have to be fit together like stones in an arch, since none of them could stand alone. Sometimes you start with one and everything else has to accrete about that, though that's very hard. Sometimes you manage to get some to work together. it can, however, get interesting. Especially if you have these bright, shining moments and are trying to figure which, if any, of the characters are repeats.