4 Basic Elements of Effective Graphic Design

These are taken from A Whole New Mind by Daniel Pink who got them from The Non-Designer's Design Book: Design and Typographic Principles for the Visual Novice by Robin Williams.

Contrast
If the elements(type, color, size, line thickness, shape, space, etc.) are not the same, then make them very different.

Repetition
Repeating visual element helps develop the organization and strengthens the unity of your brochure, newsletter, or letterhead.

Alignment
Nothing should be placed on the page arbitrarily. Every element should have some visual connection with another element on the page.

Proximity
Items relating to each other should be grouped close together.