1. Form the possessive singular of nouns with ’s.
Follow this rule whatever the final consonant. Thus write,
the witch’s malice
This is the usage of the United States Government Printing Office and of the Oxford University Press.
Exceptions are the possessives of ancient proper names in -es and -is, the possessive Jesus’, and such forms as for conscience’ sake, for righteousness’ sake.But such forms as Achilles’ heel, Moses’ laws, Isis’ temple are commonly replaced by
the heel of Achilles
the laws of Moses
the temple of Isis
The pronominal possessives hers, its, theirs, yours, and oneself have no apostrophe.
2. In a series of three or more terms with a single conjunction, use a comma after each term except the last.
red, white, and blue
honest, energetic, but headstrong
He opened the letter, read it, and made a note of its contents.
This is also the usage of the Government Printing Office and of the Oxford University Press.
In the names of business firms the last comma is omitted, as
Brown, Shipley and Company
The abbreviation etc., even if only a single term comes before it, is always preceded by a comma.