* Ensure all images are in the correct format, e.g. CMYK.
* Check spot colours have been used consistently throughout the files.
A useful check for the above is to run out all separations, this will alert you to any additional or missing colours or items in your files, to save materials you can print separations directly to a pdf file.
When sending artwork, it always helps to include a brief instructional READ ME.txt file or similar. Even the most straightforward of jobs can benefit from a quick list of items involved, filenames, colours, sizes and anything else which is relevant to each job. click here to find out more about supplying files.