Realistic head drawings will help a lot with visualization of key facial landmarks. It is also a good measuring point for the entire human body. Follow the drawing examples listed here to understand core concepts to effectively construct the head.
Usually, beginners will start drawing what they see first, usually the eyes, and then measure the rest of the head based on this landmark. Unless you have a good understanding of the entire face, this approach may lead to frustration.
Why? It is because near the final stages of any drawing, any distortion in proportions will make any type of corrections very hard to do when learning realistic head drawings. Not having the correct groundwork will lead to a lot of guessing and backtracking, especially when it comes to shading.
This translates to wasted time! So what's a good habit to get into? It's simple: focus on the whole rather than specific facial features. Specifically, the planes of the face will help you look at where to shade while the intersections will guide you to where to put the correct facial features. This is why it's important to know how to draw the head first.
Rather than burn out on the infinite amount of poses available to draw, the head can be simplified into a few common positions: front, three quarter view, and side view. Within it, there it the straight view, view from above, and view from below.
When looking at a head below eye level, the major change would be to show the nostrils, the chin structure, upper lips, ear lobe, and straight eyes. These types of deformation in the drawing will require some study as it's the most feature rich of all the poses.
They eye level poses are the most easiest. The entire head isn't distorted so it's the greatest opportunity to define facial characteristics out of all the possible angles available. The only difficult part are the three quarter view.
Looking at a head above eye level can be just as difficult as looking at the head below eye level. In this particular view, most of the details are in the nose, the rims of the upper ear, the changes to the mouth to chin structure, the hairline, and the ability to draw a neck properly in this perspective.. Therefore, this position will need careful study.
Da Vinci's sketches are an excellent source of information for learning how to draw the head. There are a lot of logical points that it makes for artists to absorb. Start with the overall head and start dividing it in halves both horizontally and vertically. These are the initial key lines needed to look at proportions.
You also need to consider proportions through age and gender; specifically, the proportions of a baby versus an adult (female). The lower part of the head is smaller because the cranium grows at a smaller pace than the rest of the head and body.
After building the initial measurements, built planes based on it. The planes on the face will allow you to see topography better. Think of planes as simplified, flat, trapezoid shapes that do well to reflect light. Start with the indentation plains around the eyes.
Then, alter the planes so it protrudes upwards and forms the nose. From there, form the mouth and then the rest of the chin. The more specific the planes are, the better sense of depth you can accomplish to help construct the rest of the head.
A typical female portrait of a young lady is drawn with a lot of care in regards to soft color gradients. As you draw your initial gesture sketch like Figure A, control your lines that it is smooth, curved, and flows well with the head.
In Figure B, you are now filling in your gesture sketch with simple value differences outlining the topography. Parts like the cheeks and the chin are areas that should be colored using a light value to pull the topography out.
Figure C is bringing the colors together. With a smooth round brush, smudge the colors together to get the soft gradient. Figure D is the final step of adding shadows and light to the female portrait where you glaze on where the light hits with a soft round brush and the soft gradients will show up better.
Where else can you find a use for this technique? If you are drawing portraits of children and young people in general, you will need to use soft gradients and lines. Therefore, it's not just limited to the female head.
On the other side of things, a male portrait has masculine lines which are not as smooth. In a way, that is why it can be harder to draw as there are many hard surfaces where colors do not blend.
In Figure A, the lines that create a masculine face is angled and usually more sharp as you draw your own gesture sketch. You want to emphasize some of the bulky sections of the face such as the chin, nose bridge, cheeks, etc.
Figure B is filling these surfaces with distinct color shades. A chalk brush is very useful here. For example, you can see clearly the indents of the cheeks are handled using a darker value. It's the same with the forehead region, nose, chin, etc.
As you can see in the next stage, blending the colors together require a hard brush instead of a soft brush as shown in Figure C. This will allow you to smudge the colors while retaining some of the hard values to distinguish masculinity.
Lastly, Figure D adds light and shadows using a soft round brush. This will give you a better overall sense of global light while still maintaining the masculine lines done on previous steps.
At this point, where else can you use masculine lines? If soft coloring are used for children and females, then this example would be great for learning realistic head drawings of older people because it emphasizes distinction of skin topography using different color values.