Sometimes when writing a book it is easy to get stuck on a particular scene or setting. It may take a while to find the right words to describe the exact mood or feeling of the moment. Or, it may be difficult to visualize the scene before starting to write it. I seem to encounter this problem at various points in almost every manuscript, so over the years I developed a technique to overcome it. I call the technique writing up "description lists".
With any given manuscript, I can usually anticipate these problematic scenes well ahead of time. Often, it may be because I have never visited a particular location before or in some cases (such as Mars), I can't go there at all. With certain settings I can usually find images online or in books that match what I want to convey. With science fiction, though, I often have to describe technology or settings that do not exist in real life. Once in a while I can find a piece of concept art that matches the idea, but other times I have to draw multiple sketches to visualize it properly.
After finding a picture or drawing a sketch, I then write up a long list of words that describe the image. The purpose of the list is to brainstorm a vast range of ideas so that when the time comes to write the scene, the descriptions flow easier.
For example, in Fractal Standard Time, I wanted to use nanobot-generated statues that could morph on command into different shapes. I had this visual in mind of the statues of Easter Island and so I printed out a copy of the one of the images on the Wikipedia page.
Then, I wrote up a list of all the words that described the image. The list went something like this: statue, rock, pumice, tall, sloped nose, oblong ears, stare, basalt, large brow, slender face, etc.
For another novel, I had to describe a painting of a forest in late fall. Since there happened to be a group of trees just outside my window at the time, I wrote down everything related to what I saw. The list included words and phrases such as branches, bark, snow, reaching, dead sticks, squirrel, leaves hanging on, brown, rust, faded leaves, dry leaves, dead leaves, crunch, forest floor, etc. Then I wrote up a list related to the act of painting: brushes, wooden frame, stretched canvas, oils, tempera, water, palette, crunch (the sound a dried brush makes when pushed onto a surface), easel, etc.
Some lists end up being more lively than others and may even lead to metaphorical ideas. The ideal time to use this technique is before you start on the rough draft of the manuscript. That way when you arrive at the points in the story that worry you, you'll have an abundance of raw material to work with in order to shape the scene.