Print and Graphic Design
There is a subtle psychology to graphic design, on the part of the customer and on the part of the business owner. Successful graphic design integrates that element.
Not all design programs, or graphic designers, are created equal. 
Designing for print
Not all designers have experience preparing camera-ready artwork for press, and that can cost you money. Calculating parent-size sheets for best cut ratio, designing bleeds to accommodate gripper edge, taking dot-gain into consideration, working with CMYK to achieve an infinate variety of colors on a 4-color press, these are all part of the science of print design.
Not all design programs, or graphic designers, are created equal. Just because you can print words and images from your office computer to your desk top printer doesn't mean the file will print on a printing press. Files created by Publisher, Word, and Powerpoint are not intended for the high-tech press environment. Desktop programs that combine images and text, such as InDesign or Quark, are better suited to smooth transition to print.
A skilled graphic designer will be capable of designing in both a vector-based program, such as Adobe Illustrator, and a bit-map program for photo manipulation, such as Photoshop. Integrating art, photos, and text takes place within the desktop publishing software, such as Quark or InDesign.
It's all in the eye
The human eye has been trained in Western culture to begin at the top, sweep from left to right, and go down. It is a natural pattern for the eye to scan in a "Z" stroke. Other elements, like color, animation, or size can disrupt the normal sweep of the eye to capture the viewer's attention.
The purpose of good graphic design is to clearly communicate a message, to create an emotional response, and to convey a solution, or point of contact for the solution. In short, it should be memorable and motivate a consumer response.