This may sound cheesy, but I won't lie: Sometimes I get ideas for a project by way of nothing but a potential piece of cover art. Remember that post from the other day about the four projects that graduated to my incubator (in a matter of speaking) this year? At least two of them got booted to incubation because I whomped together cover art for them at random. Imagining something that looked like that on my shelf made it easier for me to imagine what the back cover blurb might be, or what might be inside.
Exercises like this have become both easier and more fruitful with the advent of free-to-use, no-credit-needed image banks like Unsplash. What you create can be used as-is on the finished product; you don't have to create something solely for your own amusement and then swap it up later with something properly licensed if you decide to release it to the general public. I visit Unsplash regularly and save from it anything that looks interesting into a special folder, and a lot of future cover designs get informed by what I save from there.
Same with anything that looks like a possible character: a photo of an actor, a drawing, a piece of concept art, whatever makes me ask myself "Who is this and what do they want?" A character is a point of view plus a desire, and being able to visualize both of those things at once by way of an image brings me so much closer to the character, and so much more quickly, too.
I've mentioned before how in many ways I am a frustrated filmmaker. I never had the wherewithal to go get a camera and make movies with people -- I'm way too lazy and introverted, for one, and my life is also crowded enough with goings-on that even without us all having to huddle down in our houses I wouldn't be able to make the kinds of opportunities I would need to make movies. So I write, but one way I make up for it is by having an intense degree of inner cinema, a highly visual component to the way my work is assembled in my head. I'm still making movies up in there.
New York City
Other Lives Of The Mind