Authors often get that question.
Ideas come at all times of day and night. I've had ideas come when I'm in the shower, when I'm driving to the dentist's office, and, often, just as my head hits the pillow when I go to bed. I might see someone at the grocery store whose appearance is something I want to remember, maybe for use as a character.
I've found the only way to remember ideas is to write them down. I have a small notebook with me at all times, and I have them scattered around the house. My dh is now used to me turning the light on right after we've gone to bed so that I can jot down some plot idea, bit of dialogue or description for a setting.
I've rushed a lot of showers so that I can get out in time to write down an idea before I forget it! (Good for water conservation, too.)
Some ideas come from looking at something familiar in a new way, or really looking at my surroundings when I'm at the grocery store, post office or out for a walk in the neighborhood. I have to write down these ideas, or, no matter how good I think they are at the time, they will vanish!
I clip articles from newspapers and magazines (my own!). I sometimes "borrow" from my own life, or lives of others, with a new twist, of course.
Ideas are everywhere, but they must be "captured" before they disappear!
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