Note: This exercise is best viewed on a desktop.
There was a moment in my 3rd grade when something strange happened while I looked at the blank paper. I saw imaginary lines of a farmer in a landscape, backdropped by a field and a hut. I just let my hand follow what I saw until I finished the sketch. It was a remarkable one, given my age, still vivid until now. It's the day I fell in love with 'drawing.' This little discovery ignited into many silent games.
After then, many times, I would stare at a blank, textured wall or ceiling. The more flawed it was, the more I expect something of interest, where almost always, formations take shape. As time passed by, the little imagery goes with my mood. If I felt creepy, for sure, the walls brought out images of monsters. But I tend to see faces first and then landscapes.
Try to see an object out of nothing!
This method of staring and finding forms on walls exercised my imagination to see figures/shapes before me. Applied to drawing, stare at the paper, blink a bit and try if you can see what you want to draw. It will take time. With constant consciousness of it, you will realize that imageries do come when you need them. They naturally give surprises.
Here is how to illustrate what I mean. I tried to download some of the royalty-free images from the net. I chose grey textured (rough concrete) image maps without altering them, except for the size and rotation. The last row (see image below) was inverted, where the resulting image looks like a shabby man.
Using my Wacom Intuos tablet, I traced/doodled what I thought I saw. If you're on a desktop, look carefully at the left image map, compare it with the right image (with a Wacom line-art sketch). Get back to the left, then right again. If you think you see what I saw, then you'll agree with my Wacom sketch; or chances are, you won't see it at all.
Anyway, the derivative results are cool!
You'll notice that all the sketches were quite incomplete as they only played with the viewer's perception.
What I like most about this exercise: for some reason, images almost fall at the correct scale the way I decide how to put logic into each sketch. They are faint trails with no sense of direction unless I intervene to complete them, which naturally happens!
I see some more phantom images from the textured maps. If I let my imagination run more, I would have made almost unlimited sketches until I exhaust the entire image maps.