Nothing screams “I’m new to desktop publishing” like straight hash marks in place of true quotation marks and apostrophes. Some applications automatically convert straight to curly when importing text (as long as that option is turned on). When typing directly, use option-[ and option-shift-[ for opening and closing quote marks. Use option-shift-] for an apostrophe. In Windows, use alt-0147, alt-0148 and alt-0146 respectively.
In proper American English, periods and commas always go inside the quote marks. Question marks sometimes go outside the quote marks depending on the sense of the sentence. (The Brits put their punctuation outside the quote marks.)