As usual, my process was to begin with the outline, using fairly straight lines, then to identify the shadow line. To make this easier I drew the shadow line in charcoal on the cast itself. This can easily be removed afterwards but it's a very simple means of exploring the shadow shape on the subject you're drawing.
Having blocked in the shadow line and put in an indication of the shadow pattern in a flat tone, slightly lighter than nature, I then added the background. You can't quite see from this image, but I managed to capture this reasonably successfully - and that enhanced the sense of depth. I then deepened the shadow value to get as close as possible to the value in nature. The halftones came next, followed by modelling and turning the edges. I think the edges are probably what makes this more successful than some of my other drawings, in terms of giving the illusion of volume.
Without having a tutor around to help me, I sometimes find it helps to set myself little 'exercises' in the course of my drawing. This is what I did here. I took a photograph of the cast set-up and printed it off. I then marked in red pen on the print-out the hierarchy of edges, numbering them from softest soft to sharpest sharp, and all the edges in between. I then used this as a reference whilst carrying out my modelling to make sure the drawing corresponded to what I was seeing in nature.