Copying others’ work is one of the oldest approaches to developing one’s own skills as an artist.
For the above, I relied on carbon copies. I admit, it felt a little like cheating, because I didn’t have to worry about getting the proportions right. However, I did have to use my eyes to get down the details and to make sure everything worked in unison.
I copied the above by eye, which I think is one step away from a [stationary] model.
I drew the above using a grid, which I guess is one of those steps between relying on carbon copies and drawing something by eye.