Resumes and cover letters need perfect grammar. Here are selected rules contributed by several experts including Laura A. DeCarlo and Dr. David F. Noble.

• Laura DeCarlo's Competitive Edge Grammar Rules
  
  
• Dr. David F. Noble's Errors and Stylistic Weaknesses in Cover Letters
  
  

Apostrophe:

Don't Use: If you add an "s" to make the word plural.
Possessives of pronouns never get apostrophes: theirs, not their's; hers, not her's; its, not it's.

Do Use: To indicate omitted letters in real contractions: "do not" becomes "don't."

House Style: When a singular noun ends in s, most style guides prefer s's as in James's house. However, journalism usually uses "James' house".