i have come across this excellent web post about creating brand guides, or style guides. read this carfully and remember: following the examples and creating a proper style guide will help your client mess up your hard work less often. ;)

Designing Style Guidelines For Brands And Websites

bonus:

check out this site imjustcreative.comfor another great post on style guides with a bonus downloadable template that you can use to create your own style guide for your next identity contract.