If there is one thing I really need to say before I start: it's that no two writers ever do things quite the same way. There is no such thing as the only right way. What works for you is the right way. And what works for me is seldom the right way twice.
I have noticed a lot of people talking about story ideas... often story ideas that never turn into stories. Now, quite a lot of us are pantsers. Good luck and may the pants of inspiration guide you. On the other hand some of you are dedicated plotters. I tend to fall somewhere betwixt, but I do like to establish something of a plot outline. That varies from a detailed 50 page anal summary, which is missing the dialogue and description - the sort of thing I could turn into a book in three weeks because I've already spent a lot of time and effort on it -to a half a page of broad outline. The latter will probably take quite a lot longer to turn into a book, but for me both of them have followed more or less the same pathway. They've come from a story seed, be it someone telling me that something is impossible, or a spark provided by anything from a nightmare to something I've read in New Scientist (their physics reporting seems reasonable, some of the biological and particularly psychological articles probably need to be taken with a generous pinch of salt. But even pure manure can grow some interesting plants if you mix it with good soil.) It then for me involves reaching some kind of solution - i.e. I'm talking about a probable endpoint. I then work out a beginning. That often means writing a few thousand words which may be entirely disposable, just to get a handle on the setting and characters. It's then that things become much more variable. Basically I can scattergun it with scenes that I can see will have to happen, and try and link those up. That I'm finding seems to work better for me these days. The method I used to follow -which ended up in the 50 page outline which usually didn't survive direct contact with the first three chapters-involved systematically working from the front.
So what works for you? How do you make it from that idea spark to a viable outline? Or do you think outlines are a waste of time?