Well of course you all know ideas are the core of the book. Because if you have no idea, you have no book.
Ideas can come from pretty much anywhere. But are you prepared to take them when you get them ?
I don't try to keep them all in my memory, because that's just crazy. Especially when they come to me in the middle of the night.
ideas are a low-tech process for me. they can't wait for the computer to power up, and i hate typing notes on a computer/phone/tablet.
Plus i need to be able to get my ideas down anytime anyplace.
So i have this old notebook.
Now, i'm not some hipster and i am a writer : i have no money. So forget the stupid moleskin notebook. It's expensive and way too small (or not compact enough if large enough) for all my creation to flow.
So i use a 100 pages phonebook-type notebook. The tabs allow me to go back to each project faster.
I use at least two colors on each page, sometimes three or four, to keep track of what i edited along the way
Because one modification can seem very bad a day or two after you got the idea.
And i use pages from right to left. But that's just me being weird.
Once ideas have been laid on the page, they usually go through an excel sheet. a logical structure is laid out, be it for characters, story flow or how the book will be structured when i'm working on non-fiction.
The layout allows me to get back to pertinent information in the blink of an eye. For example, i can know right away what a particular character is, what he/she drives, what his relation to other characters is...
Then ideas are translated into text. That's when i have to get creative, to make the raw information appealing enough.