try this: pick ANY app you can draw in, pick any line-art image you find appealing, and slowly trace the heck out of it. It will teach you how to move your hand to achieve the shape. Then do the same but on a blank canvas, then trace the ref again. Repeat until you like the result when you draw it without reference (or at least when not immediately tracing over it). I use iPad + pencil v1. Recently picked up cheap stylus (still with pointy tip and battery in it) to draw on my phone. Another DANGEROUS option is to lay down your display and use it as "light table", put some paper on top of it and trace the image on paper. Though you'll likely punch holes in your display that way...