This is probably the most frequently asked question when someone finds out you're a writer. My answer to that is: "Everywhere".
Seriously.
It's like I'm swimming in idea-infested waters. They constantly bump into me, nudge me, try to get my attention in all kinds of devious ways. There's something about mundane tasks, like driving, or taking a shower, that revs up the idea generators. (Okay, I confess. Sometimes when I'm stuck on a scene, I'll take a shower or a leisurely drive, just to wake up the brain cells.)
I used to worry about losing a great idea, which is why I have millions of scraps of paper and Post-it Notes (most of which I can't even find anymore) with obscure scribblings on them, which of course means more ideas bubble to the surface as I'm trying to decipher what the hell I wrote.
My brain is always soaking up information, like a packrat that can find a use for every oddity it encounters. It never fails to amaze me how much writing occurs just from seeing people go about their daily business, or reading something completely unrelated to what I'm writing, or overhearing bits of conversation.
For example, one time while I was in the Sea-Tac airport, I walked past a bank of pay telephones (yeah, that tells you just how long ago it was), and I overheard a woman's disdainful voice enunciating to a clueless person on the other end of the line, "My husband's body is not at the airport".
Wow. All kinds of possibilities there, which of course I've written down until I can get to it. (If I can remember which notebook I used.)
Another idea came from something I misread. What I saw on a book cover was, "from one of the most rejected writers in the business". You have to admit there are so many more interesting possibilities than if I hadn't mentally substituted "respected" for "rejected".
My current WIP, I Do. . . or Die, starts with gunfire at a wedding, and I truly can't remember where that idea originated. When I attended a conference last year and Lisa Scottoline mentioned a family member being ostracized for bringing a gun to a wedding -- well, it made me feel like I was on the right track! It would be nice to say her story inspired me, but since I'd started the manuscript a while before that, I'll have to keep digging through the memory banks to see how I came up with that idea.
One of my historical romances, Lord Midnight, came about from a newspaper article I read on how the U.S. Vice President's political fortunes pretty much hinge on something happening to the President. It made me think of English aristocrats and their line of succession, and how it's a similar situation. Mmmm. What if someone tried to kill the heir, to make himself next in line? Thanks, brain -- I like that idea!
The hard part isn't coming up with AN idea. There's so many to choose from, and they can generate a rush of excitement that makes you sit down and start drafting a scene, or a chapter.
The tricky part is when the initial idea does its job, and then YOU have to decide what's next in line. That's when you go back to the cauldron, give it a stir, and see which bits collide and then bubble to the surface.
And if that doesn't give instant results, then it's time for a shower. And then a drive.
