Is it vector art? Send us your .PDF, .AI, and .EPS files.
Is it an image? Make sure it's 300dpi at fulll size and then send us your .JPG and .PNG files.
Remember: create your art in CMYK color mode, which is intended for printing. RGB color mode is intended for use on websites and screens/backlit displays.
Always convert your fonts to outlines to avoid display errors.