With due apologies to Will….
Some writers call it jumping into the mist–that is, you have the idea and you just leap into the writing, with no outline to guide you. Other writers pale in horror at the prospect of starting a book with no concept of where they or their characters are going. When I took a decade off from writing for teens and children to create historical romantic adventure for grownups, the first few books (penned as Nicole Byrd) were written with my daughter, Michelle Nicole. (Later she felt overwhelmed by life and small babies–hers–and I went on as Nicole Byrd by myself, with good wishes all around.) We had similar writing habits–except for plotting.
I have the kind of brain that jumps from point c to point g, then maybe back to f and on to p. That used to drive Michelle bananas; she wanted to go from c to d to e to f, much more logical, I admit. But my brain wouldn’t work that way, probably why I’m not a plotter, but a pantser–another nickname for ‘flying by the seat of your pants.’
I do know where my characters are at the start and where I expect them to end up (once even that changed, and I had to call my editor and explain meekly that–honest to goodness–my main characters wouldn’t do what I wanted them to, and the book was going to end differently than I had expected.  However, that book, RUNAWAY, became an award-winning YA novel.) I know the conflict that faces each character, I know their backgrounds and motivations. From there, it’s a matter of following my characters and seeing where they lead me.
Right now, I’m working on a YA novel, and the middle is frustrating me because I’m a little unsure of where it’s going. That’s the problem when you don’t outline–but as I said, it’s not really a choice. Some writers profit by having a chapter by chapter outline, and they relish its security and guidance. Some writing books will tell you a plot outline is totally necessary. But some authors just don’t work their best from an outline, if they can make one at all. (Yes, from long practice I can fake a synopsis for my editor when I need to. But trusted editors understand me well enough to know the story will take its own direction.)
For me, the most important thing is knowing my characters inside and out, knowing where they’re coming from and what conflict/problem they are facing. Then I just watch to see what action they will take to overcome the obstacles, and how they will grow in the process.
In this book I knew my main character had to end up in Egypt but wasn’t totally sure why. She has a big problem–her mother has been abducted, and now her whole family is in danger. (Always ramp up the conflict, heighten the peril as the story progresses.) How is my MC going to rescue her mother and defeat the Baddies? I’m not yet sure, but I can’t wait to find out–it’s sure to be exciting!
Stay tuned, and good luck with your own plotting, whether you outline or not. : )