The single biggest reason why files do not produce expected results is: FONTS! According to some national estimates, bad or missing fonts account for 82% of all delays and additional charges. To print your job properly, you must send us the fonts you used in your layout. The best way to avoid font problems is to follow these suggestions.
Both the SCREEN font and the PRINTER font are necessary to image your file properly. Be sure to include both on a disk with your job. Truetype fonts only contain printer fonts. "Saving for Service Provider" or "Packaging" will collect fonts automatically for you.
It is easy to overlook the fonts contained in EPS files created in Illustrator or Freehand. This is called nesting fonts and can cause problems at output time. If you do not provide these nested fonts, these characters may default to Courier or Times during output. Better yet, just converting your fonts to outlines before exporting creates a cleaner file.
When using a Macintosh computer, do not choose system fonts (these are the ones named after cities around the world). They do not have printer font equivalents and thus cannot be output on a high-resolution device.