Trees have been very influential in regards to my ability to draw the human form (and to my drawing itself). Trees and their branching nature speak a similar language as that of the human body. As tree trunks sprout branches the human torso extrudes arms, legs, necks, etc. Look to grass as it grows from the earth to better understand how hair grows from the body. Study the flow of water to better understand how to draw the invisible air.
Look to nature to unearth the secrets of drawing that no book can reveal. Look to your own nature as it forms lines on a surface, tracing your existence into shared reality.
Look at your drawings and learn from them and learn from yourself by drawing.