Know the difference between RGB & CMYK
The most obvious mistake that newcomers fall victim to is the misuse of RGB and CMYK colour modes. RGB (red, green & blue) is an additive colour system where light is used to mix colours; the more light you add the brighter and more vibrant the colour gets. When working on digital designs you’ll often be working in RGB mode because that’s how your monitor works, but the problem arises when we’re creating a design for print using a RGB based tool.
CMYK (cyan, magenta, yellow & black (key)) is a subtractive colour system where inks are mixed to create a range of different hues, much like mixing paint as a traditional artist. The more ink you mix the darker the colour gets. The spectrum of colours that can be produced by light is much wider than the range achievable by ink, so our design applications have a special CMYK mode to limit the “gamut” of the colours we have available when creating a design that will ultimately be printed.
Failing to select the CMYK colour mode and instead creating your designs in RGB may result in you selecting awesome colours that just can’t be reproduced in print (without special inks). If you don’t realise this early on you’re going to be in for a surprise when your prints come back all dull and muted.