Disguised "Construction Lines"

Characters need to feel like they live in a world, not just on your flat paper.  they should feel like they live in a world where gravity acts on them, where their clothing and armor weighs on them and they have a believable skeletal structure holding up their frame and take up 3d space.  Consider theirs a world, not made out of lines, but interpreted by lines.  their world has the variety of leather, metal, plastic, not just ambiguous liney-shapes. 

some things to help do this:

The Skeleton: Ever present, but rarely seen

-The structure underneath clothing or flesh
-no "broken" limbs
-Following the spine can help understand the Line of Action
-Check where the weight is
-see a pose in 3D space - perspective
-Believable proportions with function in mind- (can still be exaggerated, but for ex.  correctly having the arms reach just above the knees)

Hint:  Act out the pose yourself to feel where your weight shifts and how your shoulders, hips and feet point

The Volumes:

Help see the 3D shapes
How the shapes move in space
Overlaps
How Clothing lines will stretch across the shapes
The direction openings point - sleeves, boots etc.