One of the key components to creating a strong pose is the use of weight and balance.
In this simple pose, it is easy to see that the character is on balance.
His feet are firmly planted, his body mass is positioned directly over the feet, and as a result he looks well balanced and natural. It's a bit of a boring pose though. So what happens if we make it a bit more interesting? If I decide to add a bit of curve to his line of action by moving parts of his body one direction or another, the weight of the character is going to begin to shift. When it does, I have to be aware of exactly where the centre of balance is, so I can keep the weight equalized, and keep the pose in balance.
For the time being, I'm going to keep an equal amount of weight on each foot, so the centre of balance will lie directly between the feet, centred under the character's torso. As a result, if I shift one part of the character to the right, I need to shift another part to the left to counter balance it, or the character will start to look uncomfortable. Think of the body as a complicated teeter totter. Ten pounds of ass cheeks to the left? Then we need ten pounds of biceps to the right.
In these examples you can see that every time I shift the hips in one direction, I'm going to shift the shoulders in the other direction to keep the body mass centred between the feet.
If I don't, I get poses that look like this:
They still have a clear line of action, but there is obviously something drastically wrong here.
As I start to get more dynamic movement in the character, the poses get more and more pushed to one side or another, and the weight shifts until it is being supported almost exclusively by just one of the legs. This creates a new centre of gravity focussed below the leg holding the weight, and we have to begin balancing above one point, rather than keeping everything centred between two points.
The more we centre the balance over one foot, the more weight it supports. Which, in turn, means the other foot is supporting less and less, and when enough weight has been removed, it can lift, because it is no longer needed to support the body and you start to see poses like this.
Now think about a character interacting with an object. Let's say something simple, like a box. Take a look at these poses and see if you can make a judgement about what each box weighs.
Pretty simple, right?
In the first pose, the character holds the box out from his body, far to the left of his centre of gravity, and seems pretty comfortable doing so. Without any movement of the body to counter balance weight from the box, we can only assume the box is very light, and it's weight isn't enough to affect the character's pose in any way. However, with just a small shift in balance in pose 2, the box immediately takes on some weight. As I work my way through the poses I am shifting the weight closer and closer to the centre of gravity, and using the body weight to counter balance it. By the time I reach poses 5 and 6, the box has shifted entirely into the centre, and you can feel it getting heavier and heavier.
Just by having a character interact with the box, we are manipulating people into believing it actually contains something. But it doesn't. To be perfectly honest... it's not even a box. It's just a few lines on a piece of paper, and there is no real weight to it at all. I'm just taking advantage of your empathy. I'll explain...
If you draw a box alone, there is no way of knowing what it contains, and as a result, there is no way to know what it weighs. But, have a character interact with that box, and anyone looking at the pose can, and will, immediately make a judgement about it's weight. We can't help it. We automatically empathize with a character because we know what it feels like to lift something heavy. We aren't actually seeing weight, what we're seeing is a character's reaction to that weight. It's like watching the wind blow through the trees. You don't see the wind, you see the leaves moving as a reaction to the wind. We don't see the weight, we see the reaction to the weight.
It works here too.
Here the character has used a pulley to haul the box off the ground. Gravity is pulling the box directly downwards, creating tension on the rope, and in turn, pulling the character to the left. The character fights it by throwing his body weight out to the right, equalizing the pull of gravity.
Get two characters into the game and they can balance each other off. Take a look at these:
Now imagine removing one of these characters from the pose, and see if the other will look like he can stay upright on his own. Each character is relying on the weight of the other for counter balance. It's nice to have friends isn't it?
All of this is really just about keeping the weight centred over the feet, or moving it out of centre to counter balance another weight. The concept seems very basic, yet it constantly eludes people that are learning to draw.