Color separation and printing do not improve bad pictures, so try to send us your best. In most instances, negatives reproduce better than prints. Electronic files are optimal, of course. We can accept most major file formats . Note that electronic manipulation of color files imposes a color shift, based on the algorithm used to convert from RGB to CMYK color.
Contrast is very important.
Different areas of color need to have sharp edges to reproduce well, unless you are trying to show soft gradations of color. Areas of color without sharp edges will probably print a bit muddy. Very dense pictures dark reds and purples against a black background, for example do not print well. They need more contrast. Conversely, very light pictures, such as light blues and pinks against white, also do not print as well as higher contrast pictures.