…by using the natural geometry of your joints. It took me a while to figure out that it’s easy to draw lines in some directions and hard in others. And most of the time it’s simply down to respecting the pivots of the elbow and the wrist. And also why we tend to angle our notebooks so much to the desk, and why, if you want to draw a smooth line at another angle, you’re really best-off just turning the paper.
As a corollary, I figured out that by looking at angle of most of Leonardo Da Vinci’s cross-hatching you can see that he was drawing left-handed.