There are several principles of User Interface Design which construct each and every design composition. These principles include Balance, Emphasis, Harmony, Rhythm, Movement and Proportion.
Balance - A principle of design, balance refers to the way the elements of art are arranged to create a feeling of stability in a work; a pleasing or harmonious arrangement or proportion of parts or areas in a design or composition. Portions of a composition can be described as taking on a measureable weight or dominance, and can then be arranged in such a way that they appear to be either in or out of balance, or to have one kind of balance or another. Balance can be symmetrical, or formal;
Any forcefulness that gives importance or dominance (weight) to some feature or features of an artwork; something singled out, stressed, or drawn attention to by means of contrast, anomaly, or counterpoint for aesthetic impact. A way of combining elements to stress the differences between those elements and to create one or more centers of interest in a work. Often, emphasized elements are used to direct and focus attention on the most important parts of a composition — its focal point.
Agreement; accord. A union or blend of aesthetically compatible components. A composition is harmonious when the interrelationships between its parts fulfill aesthetic requisites or are mutually beneficial. As a principle of design, harmony refers to a way of combining elements of art to accent their similarities and bind the picture parts into a whole. It is often achieved through the use of repetition and simplicity.
A special form of harmony which is often linked to pattern, proportion and rhythm. It can mean
The act or process of moving, especially change of place or position, an effort. This can either be actual motion or it can be implied —the arrangement of the parts of an image to create a sense of motion by using lines, shapes, forms, and textures that cause the eye to move over the work.
A principle of design, proportion refers to the comparative, proper, or harmonious relationship of one part to another or to the whole with respect to size, quantity, or degree; a ratio. Often proportion is allied with another principle of art, emphasis.
A visual tempo or beat. The principle of design that refers to a regular repetition of elements of art to produce the look and feel of movement. It is often achieved through the careful placement of repeated components which invite the viewer's eye to jump rapidly or glide smoothly from one to the next.