So I made the following lesson for my high school art club, and thought I might as well share it here. It is meant to show how to look for and use two-dimensional relationships to improve observational drawing. I do not believe that one has to (or should) use only these 2D relationships to complete a drawing, but is something that can be used in conjunction with a more constructive method. For more detail on 2d vs construction based drawing systems read this thread:
So onto the lesson—regardless of which system you choose to use, the following can help to improve the accuracy of the drawing. I have chosen the use a drawing that I believe was done by a student of a Russian Academy.
There are two things that one can look for in terms of 2D relationships. The first is the balance of positive and negative space. This is depicted in below in green (negative space) and blue (positive space). Positive space is the actual subject being drawn, and is usually what most people are drawing and paying attention to. The shapes of the negative space as they relate to the positive space are very important and often overlooked. Negative space is especially important if it is surrounded entirely by positive space, for example if the figure is resting their arm on their hip. The negative space that is created between the arm and torso should be carefully observed.
The other aspects of 2D relationships deal with how specific landmarks on the subject relate to each other. As one becomes more proficient at drawing the landmarks become easier to identify. As a general rule of thumb though, the landmarks consist of “corners” on the positive space of an object, that is, the extremes in width and height (either convex or concave).
To start the drawing off, note the location of the extremes in height and width, and the relationships between these. The image below shows how a few straight lines can immediately set and place the drawing and set up the next steps that will take place. At this point one can note some important relationships that may be useful later on, such as the hip lining up in between the toes and elbow on the left side of the drawing.
The next few steps show lines that are not meant to be drawn, but instead observed and noted as one begins the drawing. Whenever any part is drawn, all of the following relationships should be observed.
Here are some vertical relationships between key landmark points on the figure. The leftmost line shows that on a vertical plane the corner of the head, the innermost point on the torso, the edge of the lower leg, and the point on the foot where the toes begin all line up perfectly. The middle line shows how interior landmarks such as the top of the crease in the buttocks can line up with a point such as the bottommost point of the heel.
Now the same concept as applied to horizontals. The top line reveals how the thumb lines up with where the left arm meets the torso. The middle line shows the wrist and widest point of the rib cage in relation to each other.
The next image uses the principle with oblique relationships. It can be used independently such as on the legs, or in a zigzagging fashion as at the top to really achieve accuracy. In this step it is important to also note the length of these oblique lines. If you have trouble determining the angle of the lines, hold the pencil at arm’s length and put it at the same angle. Keeping your arm straight, move it over to your drawing and compare the angle with the one that you have drawn.
So far I have dealt with angle and relationships of mostly the landmarks that are at the junction between the positive and negative space. One can also apply the same noting of angles for interior landmarks as well; below I have noted the angle between the acromion processes, the angle of the medial side of the scapulas, and the angle of the pelvis.
When undergoing the actual drawing, start off simple. Using only straight lines begin blocking in the very basic shapes, constantly checking the 2D relationships using the above techniques.
As you proceed further into the drawing, continue breaking down the shapes into ever more complicated ones as shown below. Continue to using only straight lines. By breaking down a curve into two (or sometimes three) straight lines it will be much more accurate, and help to turn the form. Once the shapes have been broken down into many small straight lines you can begin to add the curves to them to give it a more naturalistic look and prevent it from being too stiff.
I hope this was of at least some use to someone. This lesson should help to create a very accurate line drawing; shading and rendering it out is another beast that I may or may not cover later.