Form is the basis of all drawing. It is a must for any type of artwork that is trying to describe something physical, and to a lesser extent, it can also be used to describe emotions, although composition and lighting have a big (bigger) part to say in terms of describing emotion.
The most basic technique to describe form is line, and the best tool for this is a pencil.
When first starting out it is best to pick an object, put it in front of you and try and draw it. While drawing it remember to keep looking back and forth at the object and your rendition of it. If you notice something is wrong with it, try and change it so it looks more like the object. The more you do this, the more it will look like the original.
When using line, creating depth can be a problem. A way to create this can be making a line thicker when it is supposed to be close and thinner when it is further away. A better way to create depth with just line is to use different softness’ of pencil. The maximum range (as far as I know) from hardest to softest is 9H to 9B with probably the most famous HB somewhere in the middle.
The softer the pencil the stronger the line, so for example you would use an H6 for something that you wanted to show as very far away, an HB for something that was at a middle distance and a 4B for something that was close up.
Another way of describing form is by using value. You can create value by using different softness’ of pencil starting with hard (for the lighter areas) and gradually going through to soft (to create shadows). Another way to create value is through painting. My choice would be gouache (if using a traditional method) or digital painting. The advantage of painting is that you can add light and dark to create value, whereas with a pencil you can only build up to dark from light (unless you use a rubber, but that isn’t the best way to go about it, especially when learning).
After practising line drawing as well as value drawing for a while you will start to understand how things work, or how they are constructed and you will start to be able to construct objects without using reference. Here are some basic rules that should help you to draw a human being without reference.
1. A human face is not round; Try to think of its basic shape as an upside-down egg.
2. A problem people face when drawing a face is the positioning of the eyes, they will either draw the eyes too close together or they will draw them too far apart. I find that a good way to gauge the distance between each eye, is to draw three eyes in a row and rub out the middle one....so the distance between each eye should be the size of an eye.
3. Generally speaking, the upper lip will be darker than the lower lip. (this doesn't apply when the light is coming from underneath the character.
After some practice, you should be able to create something like this:
See the introduction to this mini series on The Basics of Drawing here.