Except for silkscreen and pad printing, files should be prepared in CMYK colour mode. Keep in mind that if the setup is wrong, colours on the finished product may differ from the file you sent. Here is how to set your artwork to CMYK colour mode in Adobe Illustrator.

To avoid blurriness, use only images and graphics that have a resolution of 150 DPI or more. Before sending your files, make sure to embed your images into the file.

When setting up grey elements, set the black color (K) to a percentage between 0 and 100, and keep all other colors (C, M, and Y) equal to 0%.

When setting up black text, thin lines and small elements, use pure black, i.e. C = 0, M = 0, Y = 0, K = 100).

If lines are 2 pt thick or less, use only 1 or 2 colours. 4 colours may be used for thicker lines.

To avoid issues with fonts when submitting your file(s), make sure to convert fonts to outlines, or to embed all fonts when saving to PDF.

The best format for submitting print-ready files is PDF, under the PDF/X-1a standard. Where possible, submit your files in PDF format. See why PDF/X-1a is the right format for printing.

Make sure that no elements are set on overprint, unless you need them to be.