I recently responded to a question on Quora about how to sketch simple backgrounds. The general rule is simplicity, low detail, narrow tonal range.
Here is a nice example by concept artist Thomas Romain.
If you want something to appear as if it is in the distance or in the background, you have to create what is called atmospheric perspective.
Even if its not actually that far away, its a useful tool to help create focal points in your artwork.
If you look at nature, out into the distance compared to up close, you will see that tonal ranges become very narrow as you get further away, and up close you can see the full range from dark to bright.
So, the answer is to sketch the outline of background shapes lightly, and shade them in one flat, light tone. Don’t add any dark's or highlights or detail, and don’t make your lines hard. Here is an example.
- See how the artist has divided the scene into 3 planes.The front plane has a more extreme range from deep dark tones up to the highlights.
- the middle ground where the two dinosaurs are in water, is more subtle with only a couple of tones 1 light and 1 dark.
- The background trees are one tone that has been faded out to almost nothing and the outline is very simple.
Here is a very simplified example from Lowry. The background building is drawn and shaded in the same light tone.
If you need to check this in a piece of work - your own, or when your looking at a scene, then just squint your eyes down until you can only see 1 main dark and 1 light. A good subject will have a nice range or grouping of lights and dark's.
More about this in my Notan article here.
You can use this idea in any scene so that the focus is on the main subject, even the entire subject is on one plane in space such as a single figure with no background. See below.
But if you are adding the background, it should not compete with the main feature of your drawing in terms of line weight and tonal range.
As you can see here, the focus is created using this perspective idea in the same figure and where the artist wants you to look is where you have more detail and tone. The extremities of the drawing are reduced to a simple outline with simple suggestions of detail. The result is very effective.
The further away or less significant, the less detail and tonal range. The closer you are, more detail and larger tonal range.
To get a feel for tonal range, practice the tonal scale with simple hatching and cross hatching first.
Then you can also practice your mark making across the tonal range to achieve the feeling of distance on different surfaces.