The Four Basic Principles

Contrast: To make the piece more interesting and eye catching all of the elements should be different from each other. Making them the same will be boring and people will lose interest.

Repetition: To keep the piece consistent, repeat some of the visual elements. This will unify the piece and make it more interesting, keeping the viewer's attention.

Alignment: Every element should be aligned with another, this creates cohesion and a pleasing, clean look.

Proximity: Putting like items closer together physically will make the viewer see them as a unit. By placing unlike items farther apart there becomes organization within the information.