"Something has to be Dominant."
This is the #1 necessity in design.

You'll hear it over and over again, so get used to it. A well designed poster can be readily taken in and absorbed in three seconds from ten feet away. Understanding the Visual Language will enhance your control over expressing your ideas within your work, so that hopefully you too will also get your message across in three seconds from ten feet away.

There are two kinds of lines, straight and curved.

Straight lines are considered masculine, a representation of virility and erection, and curved lines are feminine and representational of a woman's breasts and hips. It is not some arbitrarily decided upon concept but an implied psychological context of line ingrained in us over the ages. The straighter the line, the more masculine it is, and the more inanimate it is. The curvier the line the more feminine and animated it is.

From a drawing viewpoint, those parts of the body closest to the bones are hard objects and are rendered with straight lines, while deep tissues are soft and are rendered with curved lines. Take a look at your own fingers, the boney back side of each finger is a series of straight edges, while the fleshy side underneath is a series of curves.

Lines themselves have become associated with Gender, Force and Religion.

Feminine

Men are considered linear and sequential, while women are considered multi-taskers and global.
How does this support the idea of implied psychological context in lines?

The artist's job is to tell the truth, and in doing so honestly and frankly, gives rise to revelation.
(Not to be confused with keeping the practical job by doing what the client actually wants.)

EXERCISE: With another person have themlook from one side of a room to another while you watch their eyes and how the eyes travel from point to point as they cross the room. Then take a pen, hold it out and ask them to keep their eye on it while you move it from your far right to your far left. Again pay attention to their eyes as you do this. Watch how their eye travels.

What you should see is a jerky, bouncing motion as the eye jumps from one object to another when they are moving across the room on their own, and a smooth even transition while watching the pen move across their field of vision.

The point of the exercise?: "Give the eye a line to follow and it will."

Eyes roll along oblique lines easier.

Three directions can be expressed with line:

Horizontal

Direction is expressed by line, edge, or placement of objects.

Let the field (frame you are drawing in) contribute to the message.
Remember, anything right in the middle is boring