Here are the definition of 8 principles of design (according to an article from Allen Memorial Art Museum):
A principle of design that indicates movement, created by the careful placement of repeated elements in a work of art to cause a visual tempo or beat.
Subject is consistent and shows continuity of pattern.
A way of combining elements to add a feeling of equilibrium or stability to a work of art. Major types are symmetrical and asymmetrical.
Subject is centralised accompanied by straight line/curves within the frame.
A way of combining elements to stress the differences between those elements.
Elements pop out to differentiate from one another.
A principle of design that refers to the relationship of certain elements to the whole and to each other.
Subjects are compared in different heights and sizes.
A way of combining elements by using a series of gradual changes in those elements. (large shapes to small shapes, dark hue to light hue, etc)
Subject grows in a certain direction, evolving and changing its form.
A way of combining similar elements in an artwork to accent their similarities (achieved through use of repetitions and subtle gradual changes)
Subject is drawn with similar strokes/tone, sense of belonging between lines.
(Heike Andrea Grote, Flickr)
A principle of design concerned with diversity or contrast. Variety is achieved by using different shapes, sizes, and/or colors in a work of art.
Many subjects are drawn together with contrasting, randomised styles.
A principle of design used to create the look and feeling of action and to guide the viewer’s eye throughout the work of art.
Subject directs viewer’s eyes to a specific space in the frame.
While researching for illustration examples, I realised that these principles occur simultaneously. For instance, the last design for Movement also carries the principle of Gradation – gradual change in scale. These identities create cohesion in lines and allow illustration to appear ‘visual pleasing’.