In the magazine writing world, editors adopt a "house style" that covers questions pertaining to content, punctuation, and grammar. Some editors collect this information into a document called a "crib sheet." This is basically just an informal term for the writer's guidelines or writer's style book. Other common names for a "crib sheet" include house style guide, cheat sheet, writer's guidelines, and writer's style sheet.
Writing Rules and Guidelines
Crib sheets are extremely important because they outline the necessary "rules" a writer should follow when writing for that publication. Very often, a magazine (or company) will not agree with certain points of their chosen style (such as Associated Press or Chicago) and will establish exceptions. These exceptions may be published as an internal crib sheet that is made available to writers after they are assigned the work. What's most important for any writer is that they know beforehand if there are exceptions. Even if none are offered, it's best to be proactive and inquire if the publication has preferred exceptions to the rules.
A Primer on Style Guides
The Associated Press Stylebook (usually called the AP Stylebook) has been the gold standard since its inception in 1953. The go-to style for journalists and news writing, it was originally written with the newswire in mind and therefore symbols and "extras" like italics and underlining are kept to a minimum. The AP Stylebook has updated annually and has grown beyond its initial purpose. Today, writers for magazines, writers in broadcasting, writers in marketing departments and those writing for public relations firms traditionally apply AP grammar and punctuation rules. Because of its simplified grammar, such as dropping the Oxford comma and using figures for all numbers above nine, this style saves scarce print and web space.
Beyond the magazine world (whether one is a freelance writer or staff writer), there are writer's style sheets for industries such as book publishing including both fiction and non-fiction books. The standard in book publishing is the Chicago Manual of Style (or CMS) although it's worth noting that the CMS is generally not used for scholarly publishing such as journals and research.
Once you delve into the world of crib sheets it becomes a very niche category. For example, if you are writing about chemicals, there's a crib sheet for that. ACS (the American Chemical Society) has its own crib sheet on ACS style.
Practical English Usage
The Oxford Guide to Practical English Usage is also a handy guide to have at your disposal because it is easy to use because it has separate sections on word formation and vocabulary. Especially helpful is its focus on the construction of phrases with specific vocabulary words including usage of certain suffixes, such as -ible and -able and the always challenging affect vs effect.
While the vast majority of magazine writers will reference the AP Stylebook one should never make assumptions and should always check with their editor first.