The critical, crucial step is to verify your drawing, to compare it to your reference, to measure.
You can also do this while drawing from life, for example. You can draw a figure and then measure it, holding your pencil out and comparing to your drawing to find out if you got proportions or orientations wrong. You perhaps find out that way that you maybe consistently draw the head too big, and you know to focus on that. And you start to notice it, and you start to draw the head smaller, in a more correct proportion to the body.
Comparing against reference, and then fixing your drawing is, I think, the crucial step. It is where you find out what you’re doing wrong. You can be your own teacher that way and critique your own work.
Try this: after you practiced drawing from memory, keep drawing the thing many times, occasionally comparing against the reference. You’ll discover you developed a sixth sense for when a line is wrong. This is very valuable!