For those of you who have always dreamed about becoming a professional designer in your next life, we're throwing more design school 101 at you! Keep these principles in mind and your next design will be magazine-worthy.
In all seriousness, each design element (see our previous post Elements To Design By) can, and will, be evaluated according to these principles.
size relationship or ratio
equilibrium achieved by components - symmetric, asymmetric or radial
flow of elements - repetition, gradation, etc
compatibility of elements - unity & variety
point of interest or focal point