Variety: Refers to different kinds of visual content, it refers to "differences" in general. Why variety? Variety makes things interesting, without it we experience Monotony or Boredom.
  

Contrasts in composition: Contrast suggest differences between any of the elements being described. Such as size contrast, color contrast, line movement (movements) contrast, tonal contrast. Any visual element can be contrasted. Contrast contributes to clarity and variety. 
  In the picture below we can see strong contrasts in the textures, and colors, but where size is concerned, there is little contrast.

In this photograph of climbers on the Devil's Tower in Wyoming we see the similarity of vertical structures that span vertically across the picture frame. Even though there is strong similarity of the rocky "ribs" there is none the less some subtle variety in each one.

Arrangement or grouping in Composition: Generally artists will form the main objects in the composition into a kind of group. If you connect the main objects in the composition with a line you will probably notice a kind of "shape" made by the object. This is shape may be triangular (very popular during the Renaissance) or some other shape. If a person is not thinking about "grouping" the result will probably be "random" or unplanned. 
 

Emphasis in composition: The term emphasis also can be called "dominance" or dominant. A feature may be dominant owing to its size, its color, or some other device which the artist uses to draw attention to the point of focus or main interest. 

The Australian Koala dominates the picture by virtue
of the size of the figure to the space. Notice though,
line movements lead the viewer in a pathway within the
picture frame. The eye is not carried outside the frame.

Pattern in composition: For a complete lesson is pattern making techniques, please click the web link called "pattern" to see a listing of pattern making systems. 

Tension in composition: Tension is a way of creating a visual "drama" within the groupings of lines and forms. Tension comes when elements are not visually comfortable with each other. 
Sometimes lines seem to be interrupted in their paths or seem to collide with other directions of movement. Tension also comes from using certain kinds of elements that produce a sense of energy. Like bright vibrating color harmonies. Some kind of lines such as angular or jagged line. 

Clarity in composition: Clarity results from having enough focus, darkness, or other emphasis of elements. The result is that they can be viewed clearly from a distance. High contrast extremes create very vivid images. Very low contrasts create unclear images. At times artists may intentionally choose to use a "high key" effect in which all forms may be nearly the same color such as the white on white designs sometimes seen in fashion photos.  

Balance in composition: Just as when two people ride a teeter totter there is a sense of balancing weights, the distribution of objects in a picture follow a kind of system. One system; formal balance approximates an even distribution on either side. (called Formal, common in Renaissance or Classic Greek images); Informal balance is general more uneven with an area made of several small forms to counter balance a single large form. A third balance system is 'Radial' balance in which all of the elements are integrated  by a reference to a central point.