A lot of designers and creatives overlook the need for a brand style guide (also called a brand bible by some, or included as part of a brand bible), something that gives a clear set of rules for how the marketing materials should look online and offline.

Style guides can save you time, money and tons of frustration down the road, making your marketing materials easier to maintain and create. Consider it like an extension of well-commented markup. It gives you instructions for exactly how things should be done, and sometimes even insight into why.