My process isn't exactly what anyone would call reliable. I'm pretty sure it's the mark of a rank amateur, but I'd consider myself one even if my novel were published to great and wild success. I don't know if I'm lucky, or if I have an over active subconscious that doesn't have enough to do, but when I get an idea for a novel, it's like a lightning strike.
And the problem with that--the thing that makes me squirm with the idea that I'm on the road of the novice--is that no one controls when lightning strikes. I guess I ought to clarify. When I got the idea for my query bait, I literally sat and outlined how the whole story was going to go. I knew the chapter titles. I knew how it would end. There weren't any plot holes. When I sat down to actually write it, yes, I deviated. I added characters, tangled the webs (I can't help myself, I like complicated stories with conflicted people). I didn't start writing it immediately, but when I started losing sleep, laying awake staring at the ceiling, I knew I had to start or I'd spiral into sleep deprivation.
Two months after I finished that manuscript (which I had no intention of seeking publication for at the time, but that's a story for another day), lightning struck and I knew *exactly* how the sequel would go. I knew the twists of the fallout from the first book, I'd even laid out foreshadowing in the first book without knowing it. It fit that well.
Lightning struck for the second sequel, but I've put that project on hold. It seems silly to lay out all this work and effort into a project that might never see the light of day, but every now and then I dream about my MC. When I wake up, I'm tempted to go back to the trenches for that third book in the series. It's that tempting.
And these are all the good examples of lightning striking. In science these would be the eurekas of the day (most great discoveries are actually proceeded by "hunh, that's odd," for the record). Then there are the cases of the bad lightning. Sometimes lightning strikes, and it nearly shatters the resolve to tell current story.
Last night, I got struck by lightning for a book that features my MC's sidekick. It didn't derail me, but only by luck and chance. A book telling that story would, necessarily, be a sequel, so I'm saved by needing to tell the first story before the lightning story. I have a folder for such ideas, but I'm starting to wonder if I need a lightning rod for my WIP folder.
I'd like to think that the professionals all just have a little box where they keep their lightning. I imagine Neil Gaiman pulling out his thunderbolts like some almighty Zeus.