I've been wanting to do a process post for a while, so I figured I'd use my most recent self-portrait an example. This will be a continuing process through to the finish as I attempt to create a fully realized classical painting of myself from life(the key word here being "attempt").
With a medium-dark charcoal pencil, I've drawn in my head and face on a 12 x 16 inch piece of gessoed canvas board. I have my easel rigged with a small bathroom mirror so that I can easily look back and forth between the subject and the drawing. After completing the drawing of my head, I realized that the placement and composition were all wrong. I had jumped the gun and not really thought things through. So I quickly erased it all and started back from scratch, this time allowing myself the proper time to get it right using a classical method I will now explain.
When working within the confines of a rectangle, there are certain points and measurements that most humans are subconsciously aware of. Our minds automatically divide the space up into nice little sections. As an artist, we can use this to our advantage when composing an image. Before I start redrawing my head, I make sure to plot out the "armature" shown above. I start by drawing lines from corner to corner. The intersection of these lines shows me where the precise center of the canvas is. Then I draw a horizontal and a vertical through the center point. From here I continue to divide up the space with diagonals as shown.
Now the interesting thing about this funky star-shaped abomination I've just drawn all over my board is in the intersections of the lines. As you can see in the images above, if I draw horizontal (or vertical) lines through the intersection points, I'll have divided the space into exact thirds and fourths. This is especially handy if your frame of reference is an awkward measurement and doing the actual math is just frightening. The intersections also suggest natural focal points. As you can see, I decided to put my right eye exactly on the top 1/3 intersection. You can also see how all those diagonals can influence other visual choices as well (note how my entire portrait is nicely framed within the green diamond shape).
I use this method all the time when composing a painting and it really is extremely easy and helpful. If you're feeling experimental, open up a piece of your own artwork in Photoshop and on a separate layer, draw out the armature over top of the piece. You might be surprised at how much you just intuitively compose along these measurements and maybe even come to understand why certain pieces just don't seem to "feel right".
Next Step: Underpainting