Following the instruction under “the natural way to draw”, I have been practicing touch contour, in which one fixates at the contours of a subject and synchronizes the eye gaze and hand pen movement so that they move together (i.e. the pen point should correspond to the eye point all the time) without looking at the drawing (except when backtrack from inward bending contours).
So far I have found it difficult to synchronize, as my eyes tend to saccade away frequently and my hand can go out of the boundary of the canvas.
For such exercises, it is the process, not the outcome, that matters.
Nevertheless, interesting results may appear sometimes.
I was hoping to finish a normal drawing afterwards with the same subject, but it was too dark to see anything.