Here are brief discussions of 10 categories of apostrophe abuse (including one writers and editors must let stand, even though it may pain them to do so).
1. Plurals Writing the plural form of a noun in which an apostrophe precedes the plural s, such as when taxi’s is written instead if taxis, is a common error. (This mistake is known as a greengrocer’s apostrophe due to its ubiquity in handwritten—and even printed—store signs.)
2. Pronouns Pronouns are followed by an apostrophe and s only as contractions (for example, he’s). Possessive pronouns (such as theirs and yours) never include an apostrophe. The possessive pronoun its does not take a pronoun; the contraction it’s (meaning it is) does.
3. Separate/shared possession When two or more people or other entities are described as separately owning something, each name should be in possessive form: “John’s and Jane’s houses are the same color.” However, when they share possession, include an apostrophe and an s after the latter name only: “John and Jane’s house is just down the block.”