AP Style Basics
Chicago Manual of Style vs. Associated Press Style
Chicago is the oldest and most comprehensive style guide out there. Since it is so comprehensive, or because it is so comprehensive, it often takes much longer to find what you are looking for. This guide is primarily used for book authors, but because of its comprehensive nature—it’s great for everyone.
AP is shorter and clearer than Chicago. This style guide is primarily for writers who work with newspapers or news magazines.
The differences are that simple. Non-fiction writers should use AP and fiction authors should use Chicago. There are other style guides out there (Publication Manual of the American Psychological Association, MLA Handbook for Writers of Research Papers etc.) that are used for specialized writing. In order to avoid confusion you must choose a style guide that most closely fits what you are writing and stick to it. Consistency is the best way to gain the trust of your readership.
AP Style – a few things to pay attention to
a.m., p.m. - Recognize that 8 p.m. tonight is redundant. So, write 8 tonight, or 8 p.m. today. Better still: 8 p.m. Monday.
affect, effect -Ninety-nine times out of 100, if the word you use is a verb, spell it with an "a," and if it is a noun, spell it with an "e." In these two usages, affect means to influence and effect means the result of an action -- and those are by far the most common uses. Examples? Student: How will this affect (try substituting the word "influence") my grade? Teacher: I don't know what the effect (try substituting the word "result") will be.
collective nouns - In the United States, nouns such as team, Congress, committee and group take singular verbs, such as "is." These collective nouns also take the pronoun "it" instead of "they." So, if you're confused about whether a word such as "team" is an "it" or a "they," try making up a sentence using the word followed by "is" or "are." You wouldn't say "The team are playing well." Try this, instead: "The team is playing well. It may win this game." That's correct.
fewer, less - Use fewer for things that you can count. Example: I have fewer quarters than you do. (You can count, "One quarter, two quarters, three quarters.") Use less for things you cannot count. Example: I have less cash than you do. (You don't say, "One cash, two cash, three cash.")
plurals - Note the unusual rule that when you form the plural of a proper noun that ends in a "y," you usually add an "s," as in Kennedys, Grammys, Emmys.
possessives - The main AP exception to Strunk and White's Elements of Style involves forming the possessive of a singular proper noun that ends in "s." AP says merely add an apostrophe. Examples: Otis' cookies, Amos' ice cream, Charles' chips. And here's a reminder of something I'm sure most of you already know: To make something that is singular into a possessive, add 's; to make something plural into a possessive, first make sure it is plural, usually by verifying that it ends in an "s," and then add an apostrophe. Here's a nonsense sentence that illustrates the idea: One dog's bone is worth two dogs' ears.
years - To indicate a decade, add an "s." to the first year in the decade. Example: In the 1960s, I did a lot of things I don't remember. If you abbreviate this, do it this way: In the '60s, I did a lot of . . . Remember that years are never spelled out. Even at the beginning of a sentence, use a figure: 1968 was a good year, I'm told.
More quick tips
Grammar Girl Web site (great site for quick tips on grammar)