Grab something to write with and set a timer for ten minutes. Write down every possible detail you can about what it is you’re trying to do. The shape, colors, minute details, everything.
For some people this can be a simple, but to some this can be pretty challenging. But like the paragraph had said above grab something to describe on paper, and describe anything, and everything about the thing that you are describing. Think about from a author’s point of view. Specially, if they don’t have anything physical to go on, it’s all in their heads. But this is a good exercise to try.