Today I found about this Chinese painter who laid out 6 laws for drawing:

1. Engender a sense of movement through spirit consonance.
2. Use the brush with the bone method.
3. Responding to things, depict their form.
4. According to kind, describe appearances [with color].
5. Dividing and planning, positioning and arranging.
6. Transmitting and conveying earlier models through copying and transcribing.

To me, these are pointers on how to draw, how to compose and how to train yourself in the art. However, this might be wrong, because as I read, this was written using a small amount of characters. If anyone knows more...feel free to correct me.

(why these laws are important...I read DaVinci describing 'good drawing', talking about perspective and shading, but his observations were not only more technical, but also involved mathematics. It's not like the basic theory is that much different - for example, DaVinci talks about the importance of knowing the underlying structure, the skeleton, just as Xie underlines it in nr.2. It's that these older tenants can be taught easily, while Renascentist art has added dimensions to drawing)

1. "Spirit Resonance," 
2. "Bone Method" 
3. "Correspondence to the Object"
4. "Suitability to Type"
5. "Division and Planning"
6. "Transmission by Copying"