Straight line Block-In

Because the figure is exceptionally complex in its form and relationships, the wise artist always begins each drawing by simplifying it to its basic elements and shapes in order to establish it initially on the paper. The first stage of the this is the Gesture Sketch. The next stage is to establish a rough and simplified (but more accurate) version of the figure over the lightly-drawn gestural foundation.

In drawing, straight lines are easier to draw, revise, and estimate than curved lines. Therefore, it only makes sense to begin refining your drawing by constructing it from a series of quickly-drawn, "straight-ish" lines. These should be done using motor-stroke, employing long, rhythmical, sweeping lines that describe the rough proportions, angles, and positions of body parts. Do not --at this stage--try to be precise, detailed, or to draw overly-contolled contours. The idea is to capture the basic form quickly, keeping it simple so that it can be subsequently revised until all the parts are properly aligned, proportioned, and angled.

When you've completed the basic simple shapes you can start to use vertical and horizontal plumb lines.  
Plumb lines are vertical or horizontal lines that remain constant and are another objective device that will help you determine if you proportions and relationships are correct.

Don't hesitate to locate the same point by using more than one angle or measurement to assess its placement; the old adage, "measure twice, cut once" holds true here. Sometimes the technique of locating the same point with more than one angle is known as triangulation where three lines intersect at a common location. This might be the point where a vertical, a horizontal and a diagonal line intersect, or it may be where three separate diagonals intersect. This principle could be utilized in determining landmarks where as few at two lines intersect or where many intersect, as with the center of a wagon wheel.

Basically you are making comparisons and training your eye to see those naturally. Making construction lines through the figure to see what else lines up on that same line. Also its a good idea to look at the negative shapes that are created with the plumb lines to compare distances.