1. The shape must be accurate. You can't draw David in a hurry. Make the shape first. Even if it has been adjusted, you must go back to find the shape first.
2. Think as a whole. Don't think about details. Because David is big and complicated, his nose and eyes can be left alone for the time being. First divide it into several faces and find the boundary between light and shade.
3. In-depth characterization. Only on the basis of ensuring the first two items can the details be described.
4. adjust. Go back to the second step and adjust the picture as a whole.
Take a look at the pictures in the book. David painted by Yu Hong is called "the most accurate David in Asia".