Anthracene, the answer is for reference only. If it is to cope with the college entrance examination, I suggest you look at Yu Xiaodong's sketch book, which mentions that the concept of writing slowly is very useful, but it is actually a simple sketch. My understanding is: on the basis of the original line sketch, add a little color that can express the structure and texture (provided that the structure is accurate and dynamic), and just add a little. A sketch should have bright spots, that is, it should also have density and rhythm, and pay attention to the balance of the picture. This is hard to say. Sometimes you feel that the picture is on one side or top-heavy, so you should add something to the bright side to balance the picture. Finally, it is not necessarily comprehensive, and sometimes appropriate blank space will bring different effects to the picture.

I still strongly recommend Yu Xiaodong's sketches. Not only to look at the pictures, but also many parts of the text are very good ~

I hope it helps you.