So here are the questions of Jacob Cook, a high school student, along with my answers. And I’ll bet you get more answers and resources in the comments.

The key to making multi-figure scenes is to practice drawing compositions from imagination and observation, so that when you need to create a large-scale painting, you can take it pretty far entirely out of your head. After you’ve done that, you can call in the models and use photography if you want. (“Warrior Woman” was done from life studies but no photography.) Either way, let your imaginative idea guide the process.
Getting weight in figures comes from thinking about the force of gravity when you do your figure drawing. Take the pose yourself, and you’ll know things you miss when just looking at it. Dimensionality comes from a solid understanding of perspective, form modeling, and optics.
2. How much anatomical knowledge do you possess? Do you have what could be called a working knowledge of the body, or have you learned about the body at a deeper level, like the names of the bones and muscles? I ask because I'm getting to be very interested in the technical details of the human body. I've been filling sketchbooks with studies of the skeleto-muscular system, and I even bought a life-sized model skeleton to study from. I'm wondering how much of that sort of thing you've done.
I’m not really an expert on anatomy compared to some of my friends. But when I was a student I went through the standard figure texts: especially Bridgman, Peck, Vanderpoel, and Loomis. I copied a lot of the plates and learning the names of the major bones and muscles. Doing copies is a good path to understanding. The next level is to sculpt a figure from the skeleton outward, muscle by muscle. Some of the academies, such as Grand Central Academy, offer such training, and that way the knowledge really gets into your hands.
I was like you as an art student. I bought a miniature plastic skeleton, a real human skull, and a bunch of plaster casts. I also recommend purchasing a couple good ecorché figures and placing them near you in your studio when you’re puzzled over something.
3. If you're making a quick sketch of a human figure, which elements do you make sure to draw first? Which parts of the figure are essential in conveying the action of the pose? Is it the head and spine? The ribcage and pelvis? Some combination, or something I haven't thought of? Is this even the right question to be asking?
Yes, it’s definitely the right question, but I don’t think there’s a hard and fast answer to any these questions, and I don’t follow any single system, because sometimes I try to think like an animator, sometimes like a painter, and sometimes like a caricaturist. Different schools of the figure will give you different approaches, and I think you should learn them all.
Some schools concentrate on the movements of the spine and skeletal frame, others look for rhythmic gesture lines running through the whole pose, others look for contours which sweep inside the form and pick up other contours. A painter who thinks primarily tonally will look for movement and linking of tonal shapes first and foremost. If there’s a general principle, it’s to start with the big and the simple, and progress toward the smaller details.
4. In the People chapter of Imaginative Realism, you show examples of preliminary life drawings next to the finished product. But they're never exactly the same; some limb is in a different place, or the head is turned a different way. What does it take to do that with confidence? Knowledge of anatomy? Prior experience drawing such poses?
The figure studies in that chapter are works in progress--that’s why they’re not overly finished. They’re like a rough draft. You can’t get married to any idea at that stage. Often when it comes to placing a figure into the final composition, there will be a problem with how the figure overlaps with another element in the scene. Sometimes you might simplify the drapery or you might exaggerate the pose a bit more. Everything gets changed and revised all the way to the finish. Drawing the figure as a means to an end rather than an end in itself is incredibly liberating. It gives a drive and a purpose to figure drawing that guides all of your choices.
Great questions, Jacob. They show a lot of thought on your part, and I wish you well.
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Previously: Ecorche,
Anatomy of the Ear
On Amazon: Vanderpoel, Loomis, Peck, Bridgman