Ideas for books come from everywhere. Now that is not a very deep answer--but it is true. Often I will begin with the germ of an idea ... kind of a what if this happened to ... My first book, Code Name: ORION'S EYE, began as a writing project for my studies with the Long Ridge Writers Group. Taking the WWII event of the sinking of the troopship SS Cape San Juan I thought about what if the Nazis were trying to steal the secret radar equipment she carried? Then created some characters from my own past life ... and pretty soon a story began to grow.
So far I haven't answered your question in any depth. But we're just beginning. If you are a newby writer, or want to be one, post something for me to talk about that will help you.
That's it for this first venture into blogdom.