These days, most people are expected to be able to write, whether it be an essay, a report, or a resume. Unfortunately, most schools don’t focus on grammar as much as they do 'classic literature’. I’m not saying that reading classic literature is not important; they’re an important part of our cultural identity, after all. However, grammar is, by and large, the most important thing anyone should learn, second only to spelling. As a result, here are several things to consider when writing.
The apostrophe (’) is one of the most misused glyphs, particularly when it comes to the word “its” and the contraction “it’s”. Whether that’s because people forget the difference between the two or just don’t care, there’s a profound shift in meaning and tone when it’s misused. Rather than try to explain all appropriate usages, however, you should read the Wikipedia article instead.
(However, please try to remember that plural-possessives have the apostrophe at the end of the word, and “it” is one of the few nouns that does not get an apostrophe in the possessive form.)
The em dash (—) is probably one of the most important—though not so well-known as other punctuation—mechanisms for mediating flow of information. It allows for interjections to be made and sentences to be cut short. Use them wisely, however; overuse weakens their impact.
The semicolon (;) is a useful way to join two interdependent sentences not otherwise joined via a conjunction; they may also be joined with a semicolon and a transitional phrase. Finally, in situations where commas are used within each element of a list, they replace commas for separating the elements.