For me the process is a little different, depending on what exactly it is I'm drawing. For a human figure in a standard pose, I almost always begin with the head first. I was trained to do that, and so were most of my fellow students at art school, because using the head as a base metric is one of the most elementary ways of measuring out the proportions of the figure accurately. I know artists who draw figures as being 7 or 8 "heads" tall. Generally, mine are more like 6-- the bottom of the second head-length down is mid-chest, and the third is the underside of the crotch, and the legs account for the other three head-lengths. Once I get the proportions marked, I block in the figure, first in a line skeleton, then I add mass, and once I'm sure all the proportions are as accurate as possible, only then do I actually begin the work of rendering.
If I'm drawing a non-standard pose with drastic foreshortening, however-- for example, if the model is lying down so that the soles of her feet are toward me-- the rule of thumb is to begin with the front-most part of the anatomy and gradually work away from the foreground. This same approach also gets used frequently when I'm working on subject matter that isn't human.
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Mediocrity is a petty vice; aspiring to it is a grievous sin.