I had the idea of a boy who was a wizard and didn't yet know what he was. I never sat down and wondered, "What shall I write about next?". It just came, fully formed.
J. K. RowlingOH NO YOU DON’T, LADDIE!” Harry spun around. Professor Moody was limping down the marble staircase. His wand was out and it was pointing right at a pure white ferret, which was shivering on the stone-flagged floor, exactly where Malfoy had been standing.
J. K. RowlingBut some part of him realized, even as he fought to break free from Lupin, that Sirius had never kept him waiting before. . . . Sirius had risked everything, always, to see Harry, to help him. . . . If Sirius was not reappearing out of that archway when Harry was yelling for him as though his life depended on it, the only possible explanation was that he could not come back. . . . That he really was . . .
J. K. RowlingWhy were you lurking under our window?" "Yes - yes, good point, Petunia! What were you doing under our windows, boy?" "Listening to the news," said Harry in a resigned voice. His aunt and uncle exchanged looks of outrage. "Listening to the news! Again?" "Well, it changes every day, you see," said Harry.
J. K. Rowling