The Principles of Art include

movement, unity, harmony, variety, balance, emphasis, contrast, proportion, and pattern.
See some samples here.

Movement

Movement can show actions or it can be the path the viewer's eye follows throughout an artwork. On the piece on the right, the eye moves from the blue figure on the left, to the right of the page.
movement.jpg

Unity

Unity is the wholeness that is achieved through the effective use of the elements and principles of art. The arrangement of elements and principles to create a feeling of completeness. The piece looks right and finished.
unity.jpg

Harmony

Harmony is achieved in art by using similar elements throughout the work. In the painting on the right, the artist uses red color to create harmony throughout the piece.
harmony.jpg

Variety

Variety is having different contrast, emphasis, difference in size, and color. The painting on the right shows variety in shapes and color.
variety.jpg

Balance

Balance is arranging elements so that no one part of a work overpowers, or seems heavier than any other part. The three different kinds of balance are symmetrical, asymmetrical, and radial.

Symmetrical balance is when both sides of an artwork, if split down the middle, appear to be the same.

Asymmetrical balance is the balance that does not weigh equally on both sides. On the right, the large flower vase on the left balances out the smaller objects on the right.

Radial balance is equal in length from the middle, like the spokes of a tire or a spider web.
assy_balance.jpg
Asymmetrical balance

radial.jpg
Radial balance
symm.jpg
Symmetrical Balance

Emphasis

Emphasis is the point of attraction in a piece of art that draws the viewers eye. If something in a piece of art has emphasis it stands out among other shapes and lines of a drawing or painting.

In the painting on the right, it is easy to see how the artist used light to emphasize the chef. He stands out as the main focal point of the entire the painting.
emphasis.jpg

Contrast

Contrast is created by using elements that conflict with one another. Often, contrast is created using complementary colors or extremely light and dark values. Contrast creates interest in a piece and often draws the eye to certain areas. It is used to make a painting look interesting.

The piece on the right has contrast in shapes, sizes, and colors.
contrast.jpg

Proportion

Proportion is a measurement of the size and quantity of elements within a composition. In ancient arts, proportions of forms were enlarged to show importance. This is why Egyptian gods and political figures appear so much larger than common people. The ancient Greeks found fame with their accurately-proportioned sculptures of the human form. Beginning with the Renaissance, artists recognized the connection between proportion and the illusion of 3-dimensional space (perspective).

In the picture on the right you get a sense of the distance of the ship by it's size.
proportion.jpg

Pattern/Rhythm

Pattern and rhythm (also known as repetition) is showing consistency with colors or lines. Putting a red spiral at the bottom left and top right, for example, will cause the eye to move from one spiral, to the other, and everything in between. It is indicating movement by the repetition of elements. Rhythm can make an artwork seem active
repetition.jpg