Gosh, this is a rather vague question. I guess to properly answer this we would need to know in what context are you referring to for graphic design... do you mean overall websites/layout? ...or more specifically Logos or for advertising purposes?
I think generally the main element that's most important in graphic design is appeal. The image must be attractive and get attention. Preference though when it comes to designing can be different from project to project.
Graphic design is the process of visual communication and problem-solving using one or more of typography, photography and illustration. The field is considered a subset of visual communication and communication design, but sometimes the term "graphic design" is used synonymously. Graphic designers create and combine symbols, images and text to form visual representations of ideas and messages.