Crossed Wires

Here's a shorthand proportional tool you may find handy when drawing a girl (or any figure) in deep perspective.

Imagine two wooden crosshairs joined by a flexible wire with a piece of tape at the middle.  One crosshair is where the neck sprouts from the torso -- the neck root (located just above the sternum).  The other crosshair is where legs sprout from the torso -- the thigh root (located, for all intents and purposes, at the rectum).  The wire, in a crude fashion, represents the spine.  The piece of tape is at the waist, where creasing will occur.    

Why this is helpful :
-The crosshairs show the direction we're looking at the upper and lower portions of the torso, and how the shoulders and hips are angled.  The closer the crosshairs, the more foreshortening you'll get!
-The wire shows which direction, front or back or side, the spine is bent.  (Keep in mind that the spine can only bend SO FAR in any given direction!)
-The piece of tape in the middle reminds us how much space to allocate to the ribcage and hip segments of the torso.  It's too easy to accidentally elongate the torso, throwing the legs, arms and head wildly out of proportion.

Below is the above rig superimposed over an actual model, the lovely Erica Campbell.

Babe Lab Disclaimer : Non-proprietary photos and illustrations featured on Babe Lab appear for the sole purpose of review.

It's interesting to note that...
-the elbows fall at the midpoint on the wire, giving you semi-accurate proportions for the arms.
-the wrists fall at the thigh root.
-the breasts, unless being acted upon, are always parallel to the neck root crosshair.
-the neck and head can be measured up one additional segment for a rough proportional blockout.
-the midpoint moves up/down the wire in more foreshortened views.  Whichever end  is closer will be longer, and whichever end is further away will be shorter.

When using the "Crossed Wire" rig, play with :
-the distance between the crosshairs (adjusting their midpoints accordingly)
-assigning the neck root and the thigh root to different crosshairs (essentially reversing the viewing angle or body orientation)
-angling the crosshairs to show tilted shoulders and/or hips