Odd ideas come to me from time to time. I have a file on my computer marked 'random ideas and bits'. Into this go any scraps of ideas, any half remembered dreams, links to interesting news stories. Whatever catches my eye, really. If it caught my eye, it's because something in that idea/story/article chimed with something in my subconscious. Next year, when I'm trying to think about what to write, I'll go through all the scraps and see what ideas I can tease out and develop into a plot.