Use the serial comma (the final comma before the and in a series of three or more items).
The colors in the American flag are red, white, and blue.
Use an unspaced em dash (—).
The physical impediment will lessen—perhaps even disappear—in time.
Order of punctuation
Periods and commas are always inside quotation marks.
Form the possessive of a singular noun ending in s by adding an’s:
Charles’s not Charles’
Use three dots (…) for an ellipsis, whether a sentence has been left out or not. Always provide a space either side of the ellipsis.
Abbreviations that are formed by using the first initials of separate words should not have any periods after the letters:
No periods ...