Sketching is to learn perspective and proportional relationships, and to guide the depiction of shapes based on this theory. Then repeated paintings, the purpose is to compare the direction of the line and other points through the line, through the horizontal and vertical multiple comparisons can finally draw.
Summarize the shape, first and then round. If the object is rounded, it is directly summarized by a circle, and the overall remedies are directly summarized into a square. When you combine a still life or an avatar, you should also start from the overall generalizable perspective.
It is really impossible to draw a tool. Hold the pencil up and hold it straight, and lift it to the center of the vision and the object.