A friend of mine brought up my collage composition.
Figured we can start by talking about small elements I use for filling background.
Example:

聊起杂志类构图，可以从聊如何用部件糊弄背景开始。
举例：

Collage compositions are the composition I use only when drawing for other people, aim to quickly please others.
I don't like drawing in this way for myself.
Since the goal is to get the result quickly, my approach is adding elements that are not too complex to steal the spotlight, but look nice enough to have a bit info.
Break into details:

杂志拼接构图是给别人的图 + 营业专属构图，是【为了快速讨好他人】而搞的。
自己其实不喜欢这么画图。
因为快速讨好，这类构图的中心思想是捣鼓【单看不会像画的主角一样复杂，但有些信息】的小物件。非常随心。
拆件：

Outline the object, referencing real photo, and using brushes with patterns all are common tricks I use.
For making colour harmony, slightly adjust the hue of nearby objects to avoid clashing.
As long as the background is white-ish, it can't really go wrong when all items look good in it.

【物体描边】【临摹色彩照片】【带图案的笔刷】都是常用的偷懒好手。

为颜色和谐，临近的物件会调整下色相，避免冲突。
只要背景是万金油的白色，把好看的东西放上去基本不会出错的。

Compare to draw a character, and then emphasize the cool part of the character, I personally prefer do some cool composition and put the character in it.
Also I favor simple geometric composition.
Instead of talking about how to draw the background in these cases, both the main character and background are part of the composition.
I force myself to aware that I am drawing the whole illustation, instead of drawing specific element, I need to think about them together.
Then pay attention to step few meters away from the computer time to time to check the overall result.

自己起构图比起【要画个角色，要突出角色的酷】，喜欢【来点酷构图，然后把角色放进去】。
非常偏爱一些画面简单的几何组合。可惜近几年没在画…！
比起讨论如何画背景，觉得角色和背景都是图的一部分，会注意【我是在画整张图】而不是【某个物件】。会一起思考。
也会注意时而离电脑远些检查效果。

If composition occupies the full canvas, the overall effect would be easier to be comfortable.
Not only the placement of the volume of the objects (Fig. 2), but also the position of the shadow divisions and the arrangement of the colors (the red chair in Fig. 3) can be used to form the composition.

构图横跨占满全画布。整体效果会舒服。
能展示构图的不止是物品体积的摆放(图2)，包括阴影分割的位置，颜色的安排(图3的红色椅子)都可以拿来组成构图。

And for my own oc drawings I like not drawing their front face ...
Love the air, the temperature, the sideways depictions.
Illustration is fun, there are many different approaches all direct to archiving emotional resonance.
For example, if I want to draw the emotion of nostalgia.
I could put a rustle filter on lines.
Or I could go for very, very light colors, not make it not looks realistic.
Slanting strokes like the one in Fig. 2 can also achieve the sense of light coming in from the window.
These are a lot can think about when composing a piece.

而自己的oc私图喜欢一些不对着脸画……喜欢空气，温度，侧面描写。
插画是一件有趣的事，很多不同方向的处理方法都能引起感情上的共鸣。
比如想画【怀念过去】的情感。
可以用线条下手，在线条上加沙沙的滤镜，不让它真切。
也可以选很淡很淡的颜色。会感到恍惚。
像图2斜着的笔触，也能达成光射进来的空气感。
这些都是可以在构图时思考的部分。

In the past I once signed up for let's-draw-from-photo event to practice the color of the background.
It turned out that drawing real landscapes as backgrounds was more about how to deal with shapes and textures than just the colors.
For example, should I add ripples when painting water and how. How should I deal with the shape and the thickness of clouds.
How about smoke, grass, fabric, flowers, etc.
Since I didn't get it at all LOL. So I went down a crooked path of processing real pictures into backgrounds.
After a long time, I came cross the term landscape sketching.
Oh, so there's a whole subject about working on these. No wonder I didn't figure it out.
But processing real pictures works pretty well as a shortcut....

以前报过一期色彩班长，画了一半。是个照片临摹活动，想练练背景的颜色。
结果发现以真实风景当背景，比起颜色，更多的是物件和质感的处理。
比如画水时要不要加波纹，怎么加。如何处理云的形，云的厚度。
烟雾，草丛，布料，花海等等等等。
我因为没搞懂于是走上了一条【处理真实图片当背景】的歪门邪道，后来才学到了【风景速写】这个词。
原来这些东西都是要一个一个去思考攻破的…！都有了风景速写这个系统理论。
不过处理真实图片作为逃课还挺好用的…

I haven't figured out this shortcut trick completely, so won't go into detail here but share some thoughts.
Real photos don't look like paintings because there is too much information and too nosiy.
The easiest way to do is to use blur to reduce info.
But blur is an effect is that hard to edit again. Adding any non-blurred strokes will look disharmonious because it's too clear.

这个逃课技巧我也还没摸索明白，这里不详细讲了，提供一下思路。
真实照片看上去不像画是因为信息太多，太吵了。最简单可以用【模糊】处理。
但模糊这个效果又【很难再度编辑】，因为再加任何不模糊的笔触上去会因为【太清晰】而大打架。

Therefore I use cutout and trace contour with adobe photoshop a lot.
Cutout is for reducing real photo's colour amount, on the other hand trace contour can get lineart from the photo.
I used to think that the photoshop magic was a one-click-bang!-done type of fliter, like instagram's filters.
It took me a long time to realize I should use them in combination.
For example, the role of cutout is to categorize the image into several colors, after we get few color blocks, we can edit them one by one for colour adjustment.
The trace contour will extract the lines, we can trace more than one time with different result, and then change colours, and so on.
Since I'm not a photographer myself, still want to go back and learn how to deal with various backgrounds when I get the chance...
What's all for part 3, thank you for your reading : )

我常使用的是photoshop的cutout和trace contour。
cutout减少颜色数量，trace contour提出物体的线，在合适的地方再使用。
我以前以为ps的魔法是像ig的滤镜一样一键出图类型，后来才想明白ps处理方式只是方式，不是【嘿我能把图片变成这个样子哦牛逼吧】，是可以组合使用的。
比如cutout的作用是把图片归类为几种颜色，归类完的几种颜色块，可以一个一个进行调色。
trace contour会提取出线，细节多的线和细节少的线可以分别提出，变色，等等。
因为自己不摄影，有机会还是得回去学学如何编各种材质与背景…
以上，感谢阅读。