It's important for the manual's users to understand the philosophy behind the standards. Whenever you're assembling a new standards manual, make certain to leave a prominent space for the statement of purpose. The best place is the first page after the inside-front cover and directly before the table of contents. This way, the reader can't get into the manual without at least acknowledging the philosophy behind it.
Brevity is the key when assembling a standards manual. Keep descriptions and explanations short wherever possible. Work with the manual's editors to cut down long explanations to just the bare bones the readers will need to know - no more than two or three paragraphs. This will make the rules easier to digest and remember.
Provide visual examples of the standards outlined in the manual. This is easy when the manual is centered on something visual, such as a design style book. When the subject is something more abstract, like a grammar style book, use type treatments as a visual. If one of the standards in the manual is a prohibition against the Oxford comma, show an example of one in a larger type that's noticeably different from the regular body type. For something like a customer service manual, try to have small drawings or vignettes illustrating both proscribed and prescribed behavior for employees.
Probably the most important thing to remember when laying out a standards manual is to adhere to the standards in the manual. Nothing is more undermining to a document as a blatant ignorance of the rules within. If the standards manual prohibits type on gray color screens, don't put type on a gray color screen in the manual. Readers will be less apt to abide by rules in a document that breaks them.
Have a dedicated page toward the back for credits and contact information. Make certain contact information for everyone listed as having helped assemble the standards manual is on this page. That way, when someone in the company has a question about the rules in the manual, or a rule they think should be in the manual, they'll know who to contact. It might also be a good idea on this page to actively solicit employee feedback for ways to improve the manual's content and layout.