Work in the Right Software
Prepare your art in the program that is best suited for the task. Illustrator® for vectors, Photoshop® for raster images, and for multi-page documents use a page layout program such as InDesign® or QuarkXPress®

CMYK or RGB
Remember that offset printing requires that all files be in CMYK to separate properly. For stock images that are usually supplied in RGB mode. Keep in mind to convert colors to CMYK before printing your file!

Trust the Software, Not the Screen
If you are doing color corrections or manipulations on your own, rely on the numerical color gauges in Photoshop® rather than what you see on the screen. Your monitor might not be well calibrated!

Use Hi-Res and Low-Res Appropriately

Typically, the resolution should be 300 or 350 dpi for Hi-Res output