Yet I have also written full novels that had no story. It was fun to write but nothing anyone else would read. Other times I have begun with a great idea and then struggled for each word after a couple of weeks. In both cases the idea called me strongly but the revision process often changes the entire story. I want to win NaNoWriMo and I think you do too. Here's how I grab the vision that will carry me to a win.
Stories are about People who are Somewhere and have to Struggle.
Science Fiction and Fantasy authors can have a very wide definition of "People" while historical novelists are more limited. For this to work your People must feel; they must be imperfect, limited, and subject to emotions. Readers are People and they want to identify with your People. Dealing with People can be messy; that contributes to your story. To define your People means getting into their head and understanding things from their view. That means your People may not see exactly like you and they may not even see the same things as you. Different People in the same story can see the same thing very differently. Think about your People; what do you like about them? What could they improve? Why to others like/follow/hate them? If you get stuck, pick up a copy of "GMC" and build the charts. The more time you spend with your People now the easier they will be to write about.
Where are your People? London in 1899? Pennsylvania in 1787? On a classified mission in 2019? Aboard the "Strouden's Moons" command ship in 1416 (Star Confederation Calendar)? I have a lot of fun writing about places I have been that I loved or places I'd love to be but have never been. Your People must be Somewhere and your reader will want to be there too. Historical and Modern Day authors have the advantage here; there are lots of resources to explain living almost anywhere on the planet. The Urban Fantasy writers get the best of both worlds; a wide definition of People and a lot of descriptive resources for the Somewhere those People wind up. Your reader will want to share your joy in the Somewhere that you describe, describe it well! Physically walk there if you can; absorb the sights, sounds, and smells. If your Somewhere is distant, improvise. When I was writing about star ships I spent time on wet navy ships to get a feel for the setting. The more you can integrate Somewhere the more your reader will want to return to your creation.
Readers pick up an unfamiliar book because they want to see what is going on; what the Struggle is. The meat of story is simply about People, Somewhere, who Struggle for something they don't have. This is where I have had to work the hardest. I mentioned "GMC" above, if you have the internal and external conflicts thought out then you have the basis for Struggle. Struggle provides energy for your story and interest in your reader. Struggle uses the identification a reader has with your People to give the reader a wild ride through the entire book. Pages will turn with haste as the reader wants to know what happens next...who does what...do they win? When you have the People and the Struggle you can use the "Writer's Journey" to build a framework for what happens when. The structure transcends genre and forms the basis of what your reader expects. Following the structure in your story means your reader is free to enjoy just the story; they don't have to figure out an entirely new structure as well. Your reader prefers a good story told along familiar lines.
People, Somewhere, Struggle.
Pick what intrigues you most and start there. If you like a certain setting, figure out what the Struggles are in that setting. Who felt the Struggle the most? Which People do you want to write about? Or set aside preconceptions of Somewhere and focus on the Struggle. What People best identify the Struggle; where best shows it? These sorts of open questions prod your brain to come up with its best work. Start early, well before NaNoWriMo. Give your brain time to better percolate your novel.
Revel in the preparation for NaNoWriMo!