Start with what you do know: The world around you. Use your 5 senses.
For a sunset, look at a sunset at your home then start thinking about how it would look. Is the sun the same color? Is there more or less pollution? Fog? Dust?
What types of buildings do you see when you look at the sunset? Would those types of buildings be there? Different buildings; what type? What do the buildings look like in your world? Maybe there aren't any buildings. What is there instead?
Now start going into detail, look at the pieces of what you see:
For Example, look at the roofs of the buildings. How would the roofs be different?
What kinds of sounds would they here? On a space ship, would the life support be silent or where there be a constant background noise? How about the sound of the engines, if any? Are the doors silent or do they make noise? How far away can you hear the noise? Huge metal doors can be heard from quite a distance and the clang would be transmitted through the hull. Characters might be able to identify different doors on their ship from sound. A Star Trek door makes sound but one wall between you and it would block that sound.
Think of the smells. The midwest smells different from the west coast because the moisture and soil are different. Pollution has a smell. Wood cook fires have a smell. Plastic has a smell.
For touch, does the ship have a constant vibration? Is it hotter or colder? Drier or damper?
You can probably forget taste, unless your character likes to lick the scenery (I am not reading that story).
Go down to as much detail as you can. Not all of this detail needs to go into the story but it'll be there, influencing the characters.
Remember that people, thus your characters, tend to focus only on what is immediately important to them.
You can start with a scene where someone is fixing an engine. Then he feels a breeze that provides a welcome relief from the heat but it has the smell of moisture in it. Now, can he finish the front left nacelle of the hovercar before it rains or should he spend his time dragging the tarp over it? He looks up in the sky and sees....