Some days they just flow from everything. I read one of my group digests and they mentioned writing exercises and gave a list of fake news article titles. (I'm warning you now that I'm very sleepy and will probably make lots of mistakes on this, but I'm going to gut my way through it. Sense it might not make, but at least proud Yoda will be.) So jump on board my idea train of thought. One article title was Fireman rescues Woman and Four kids. This can generate all sorts of ideas with these six characters, but I have a convulted mind. First off I don't do kids in my books, yet. I just don't. So lose the kids and you have Fireman rescues Woman. Big deal. Where's the conflict in that? Well, what if the woman doesn't want the man to save her? What if she'd rather die a firey death than let that man touch her? There's the start of a conflict that can be expanded on to make a story.
Then I'm sitting watching TV and I catch the last bit of a show on UFO's and some strange man is making a case for what he believes. The TV fades into the background as my mind races with the concept and twist it into something that could potentially be a story. I pop open word and type away and the initial concept turns into an interesting mystery.
Ideas come from anywhere. I'm grateful I don't have issues with coming up with ideas. Basic ideas for stories. Now creating a cohesive plot using that spark of an idea, that takes time and brainstorming. To plot a new book takes me at least a week to a month. But those little sparks that say hey, I could be a story, those are easy once you know what you are looking for.