I've read millions of ways different authors pull the ideas and thoughts out and turn them into the magic we read on the pages of there books. For me the ideas are all small pieces that come to me one at any given time. The family origin, the number of people in the family, the time of year it starts, the places they will go.
All those things go into what the story will be and then from there I start an outline idea with all the different parts put in there to show me the story....Then of course my fingers take off whether they are writing the words in a notebook on typing them on a keypad they speed across whatever surface needed till there are no more thoughts left.
But by far the biggest motivator for me is now and forever will be music....my many different playlist motivate me they give me vision and outlook...so when i need a story i simple let any given playlist run and let the thoughts come.