To maintain some kind of standard, I just did that. I stared at my closet door for a minute, and I imagined 5 different visual/story ideas, and they were all based on details of or defects in my closet door. (One was a strange pattern of tall, thin windows that give a view of the seaside; one was a bird's eye view of a dad wearing a long, blue dress jacket walking over a desert of dried paint and falling face-first over a large lump of paint that, to little him in that great white paint desert, is almost a hill; one involved a virus spewing like steam out of a cut wire; one was a sliding door on a cozy spaceship; and I forget the other one, but let's take another and say a closet is covered by a big rectangular granite slab that has misshapen eyes near the top, and maybe that kind of interior decoration is fashionable in this time and place.)
It's like asking, "Where do you go to listen to NPR?" That's fine for a person curious about your habits, but otherwise it shows a misunderstanding of the availability of NPR. If you've got a working radio, you just turn it on and tune in, wherever you are. If it isn't working, or you don't have one, you go and get one, or get it fixed.
The most basic trick to ideas is to stop worrying if it's a great idea, or if it works, and start pulling around the clay in your mind, the clay of all those sensations and memories, and, yes, whatever is in front of you at the time. The weirder, queasier, more outlandish, more half-formed and emotional and impossible to describe, the better. If it's terrible, that's like stretching before a run. There's no shame in it. Ignore any suggestion there's shame in it.
Sometimes an idea will punch you in the gut from around a corner you don't even see.
For example, two days ago, a student mentioned... what was it... ah, the French Revolution, when the revolutionaries wanted to change everything, including the calendar. So they adopted a completely new, bizarre, unfamiliar calendar. And it quickly fell through, because no one got used to it. Were the weeks even 7 days? I wanted to find out more. It excited my imagination. I said, that's a really interesting opportunity for a story, that moment in history, the bewildering calendar, what happened.
And I know I'm right.
What did that take? Almost nothing. It's like going to the supermarket. Go there, you'll see things you can eat. Except... the supermarket is everywhere. "Where is the supermarket?" happens to be exactly the wrong question. Where I S N ' T the supermarket? Now we're talking. Now we're cooking with gas.
There's this misconception that unless you are very responsibly worrying all the time that this idea won't work, you won't come up with any ideas that work. Totally wrong. Just come up with ideas. Don't shut off all critical thinking always, but suspend it sometimes, sometimes completely. And don't be too quick to kill something that doesn't pass the critical filter when you turn it on. Often it just needs tweaking or reimagining.
There's no shortage of people in the world who will delight in telling you what they think is wrong with your idea. They won't always be wrong, won't always be right. And you'll need to do some of that work yourself, a lot of it. But you are being different from them. You can do more than just shoot an idea down.
The biggest mistake most people make with ideas is confusing familiarity with plausibility. In cognitive science, that's sometimes called the availability heuristic. Basically, you try to imagine a thang, and if you run into any resistance, you conclude that this indicates the thang is not plausible. For example, if you are really straining to imagine that Puerto Rico could ever become the 51st state in the US, then you may conclude that this means it is correspondingly unlikely to happen, or unlikely to work if it does start to happen. Conversely, if it's easy to imagine your neighborhood's nuclear power plant melting down and spewing radiation all over the continent, or your next flight losing both wings and crashing into the ocean, you conclude that's very likely.
Just reminding you to remind yourself, then: "imaginability" is a well-known and carefully studied fallacy. Your brain is not half as good at all that as you assume. You are often enough drawing the wrong conclusions without realizing it, just on the basis of ease or difficulty of imagining scenarios. To put that differently: on the basis of familiarity.
If you've ever described new ideas to people, you have run into this. Even if the thang is true, even if it works, even if you know this, people will push back because they have trouble imagining, and they are sure this must mean it just isn't realistic at all.
Don't do that, and you're already a million miles ahead of most people. Notice that isn't a place you go! It's just watching out for a bias and shooting it in the head when you see it. With a Nerf crossbow. But it'll get the idea and leave you alone for a few minutes.