Gradients
A gradient is the transition of one or more colors from dark to light. They become problematic when the color varies too little over too large a distance or when the gradient ends in less than 5 percent of a color. Gradients without sufficient variance between the light and dark color may appear banded when printed. Banding can be completely avoided be creating gradients in Photoshop and adding noise. The noise disperses the dots, minimizing or eliminating banding.
Transparencies
Be conscious of the stacking order of element when using transparency, as this can affect the print results.
Drop-Shadows