Page 1: Introduction
The Principle of Repetition states, "Repeat some aspect of the design throughout the entire piece." The repetitive element may be a bold font, a thick rule (line), a certain bullet, color, design element, particular format, the spatial relationships, etc. It can be anything that a reader will visually recognize.
You already use repetition in your work. When you make headlines all the same size and weight, when you add a page number a half-inch from the bottom of each page, when you use the same bullet in each list throughout the project - these are all examples of repetition. What beginners often need to do is push this idea further - turn that inconspicuous repetition into a visual key that ties the publication together.
Repetition can be thought of as consistency: As you look through a sixteen-page newsletter, it is the repetition of certain elements, their consistency, that makes each of those eight pages appear to belong to the same newsletter. If page 7 has no repetitive elements carried over from page 4, then the entire newsletter loses its cohesive look and feel.
But repetition goes beyond just being naturally consistent - it is a conscious effort to unify all parts of a design.
Source: The Non-Designer's Design Book by Robin Williams