As a parent and creative professional, I think it's easier answering the stork question. At least for the birds and bees, there's an actual answer. As uncomfortable as it may be.
Anyway, I often ask myself that very same question ... just where
do these ideas come from. Even as they emerge, I'm not all that sure from
where they arrive.
Sometimes they just do. But that's not to say it's (all) magic.
It's not as if I sit around like Pooh, tapping my head and saying "Think. Think. Think."

For me, developing the killer idea is more about putting
yourself in best position to
receive it, as opposed to actively seeking it. For more often than not, this happens out of office and away from the work environment. There will always be idea time in the office, but keep an open mind to those opportunities away from the work setting.
Consider:
1.
Exercise. Nothing like an hour on the treadmill or three hours on the bike to get the
creative juices flowing. Maybe it's the endorphins, or maybe it's just the mind-numbing scenery (or just not having the phone ring for a while), but I've had more
aha moments while exercising than any other way (think how successful I would be if I exercised enough!). You don't have to pressure yourself to have great ideas within the next hour; just recognize that you have a great opportunity ahead of you to develop a needed idea or solution to a knotty work problem. Tip: if you're on a stable machine, take along a note card and small golf pencil and jot the ideas down as they come.
2.
Driving. Probably for the same reason as above. Whether you need the radio or not, the monotony or while line fever can draw your mind into a well-positioned place to receive great ideas. Tip: pull over before you write!
3.
"Active Nothing." Oxymoron? Yes. Effective? Sure. All this means is taking a few minutes to unplug the TV and the computer and "do some nothing." Doodle. Walk. Vacuum. Rearrange the stack of magazines. You'd be surprised how open your mind becomes to ideas when you're engaged in a bit of nothing.
There is always merit for creative and strategic brainstorming, yet by just taking a break from the traditional work setting, you may find your mind in
receive mode.Just my idea ... what do you think? What are your best "idea settings?"