The third tutorial in the series.
Seeing basic shapes
Human body has always been one of the most fascinating subjects of study for artists. It's also very complex thing, so drawing human body may seem overwhelming at first. However, this is where simplifying kicks in. When drawing complex things, you first need to break it down into very basic shapes, such as cubes, cylinders, spheres, cones and so on. It's significantly easier to sketch things quickly with basic shapes than actually render the details exactly.
Drawing basic shapes may be boring, but it's really useful practice because you can't really get away from perspective. And as simple as it may seem, it's not that easy to draw even those basic shapes right at first. It took me a lot longer to draw that row of basic shapes than I had expected. It was surprisingly good practice even for me.
Once you are able to draw individual shapes, you can start mixing them together to represent more complex things, such as human figures. Also, you can use a box as a guide and draw more complex object inside it. Using reference objects is very useful.
Seeing the planes
In order to truly understand the 3D, you will need to understand where the surface actually faces. This is where basic shapes come handy again.
You could say that the "curvature resolution" in human figure is so high that everything appear very smooth. However, it's quite hard to tell which way the surface is actually facing. A cube, on the other hand, is pretty easy: it has six faces, so they face six different directions. Smooth surfaces can be simplified into more blocky forms that make it easier to see the planes. This will also be extremely useful when you are applying shadows. When you are familiar with seeing planes, applying shadows will come naturally to you.
I usually use middle lines to determine the planes, sometimes contours with more organic shapes. With the two human figures, I wanted to illustrate the planes. I hardly ever draw things like that, so it was pretty refreshing to do. I also like to draw the characters like they were action figures xD.
Note, that while human figure drawing requires general understanding about perspective, it's not always necessary to construct the perspective. I find that the perspective guides are very useful, but once you can see three dimensional shapes and understand how we truly see (see my first tutorial), you won't really need the guides. I find that drawing doesn't need to be perfect, as long as it's convincing.
Remember that these are drawn for illustration purposes. You don't need every single guide when you are sketching. Once you are familiar with the 3D shapes and planes, you can drop quite a lot of the guides. I included some sketches there to demonstrate the roughness (I'll cover dynamism and foreshortening later). If you want to know more about the guidelines, search some other tutorials.
Proportions: heads as a measure
One common way to determine the proportions of the human character is to use heads. That is, how many heads stacked on top of each other would it take to equal the height of the character. An average adult human is around 7 - 7.5 heads tall. In illustrations, very epic characters tend to be as tall as 8-10 heads tall. Super deformed chibis are often around 2-3 heads tall. I often draw my female characters 5 - 6 heads tall for more cute proportions. I also scale some body parts to exaggerate the feminine body shapes.
There are a lot ways to determine the placement of each feature in human figure by guides. I haven't really used other than heads much at all. I have used more detailed guides on facial features only, but I have settled to very simple rules: eyes are around halfway, the ears are on eye level. The mouth/nose is around 1/4 head from chin and the earlobes are on nose level. Also, the distance between the eyes is one eye and half-eye from the outlines (forgot to illustrate this though ^^').
Remember, that the number of heads has nothing to do with the actual height of the character. It's just determines the head size compared to the rest of the body. That said, a character with 3 heads can be as tall as character with 8 heads. The difference with the proportions is just tremendous.