I've heard so many people say that they "aren't creative enough" to design things, or that they "don't have ideas".
If you've ever had a thought, if you're aware of your surroundings, and if your brain works even in the slightest you have ideas. They might not be good ideas, but they're ideas.
How do you come up with good ideas? You practice by coming up with bad ones! When I was a kid I read that we all have a million bad ideas inside of us, and the sooner we can get them all out the better. So even if something seems stupid, go for it. We learn by doing, and you'll soon find that working with one idea will cause you to come up with another.
For some reason, knitters suffer from the delusion that you have to be a capital-D Designer to come up with an idea or make an original garment.
Designers (even the famous ones) are human just like the rest of us. They sketch, they write, they knit, and I'm sure they occasionally forget to put in a lifeline and have to rip back a lot farther than they should have. What seperates a designer from a garden-variety knitter is a willingness to try new things, to experiment, and even to fail. A designer looks at a simple idea and sees potential.
I'm going to help you learn to see potentail, starting with a simple concept.
This is my sketch, just a series of rectangles I doodled. As they get bigger, the space between them gets smaller.
You could have come up with that, right? Exactly! Ideas are everywhere, and sometimes the simple ones are the most effective.
When you look at your concept, think about what it could be. I could take this as it is and make a Modernist painting. I could line up appropriately-sized objects and create a still life composition to draw, paint, or photograph.
I started out with a simple, literal interpretation: I made it into a three-dimensional form, it could be an entranceway into a building. The empty spaces gradually get smaller, transitioning a person from "outside" to "inside".
As I was drawing that, the angles made me wonder what it would look like if I took two of my concept sketch and rotated one 90 degrees. I sketched it out quickly and got a pattern that reminded me of tartan.
To refine it a little more, I made a more finalized drawing in Photoshop. I could print this out as digital art, paint it (which might be interesting with some really texturized paint), turn it into a woven or knitted fabric, or use it as a layout grid for a graphic design.
As I was thinking about how I could knit that (I know nothing near enough about colorwork to puzzle that one out, but maybe something reminiscent of the Ball Band Dishcloth), I had another brainstorm: Lace!
This is just a quick, sketched chart I drew that alternates solid stockinette rectangles with rectangles of yarn-overs, the simplest type of lace. The rectangles change in size and frequency, just like the original concept sketch. The next step here would be to swatch this and see if the proportions work out, and to alter it if they don't.
Ideas are everywhere. And design is just a methodical approach to "playing" with ideas, moving them around and changing the color and seeing what concrete things you can make of an abstract concept.
A great way to get visual ideas into a workable format is to take a photo of something (a line of trees, spokes in a wheel, the shape of a building) and trace the important lines and forms. Then you can work with that and see what comes of it. It takes practice, but you'll find that the more you do, the easier things get.