When you join three or more elements in a series, put a comma before the conjunction (usually and or or). Thus: red, white, and blue. This is the serial-comma rule. The comma is also referred to as the Oxford Comma. The top style manuals follow the serial-comma rule. So should you.
The series may consist of any grammatical element. You can construct sentences with three or more subjects, verbs, direct objects, objects of prepositions, verbal objects, or any other grammatical part of a sentence. In the following examples, you'll find a variety of grammatical elements appearing in a series. Each is named parenthetically after the example.
The flag is red, white, and blue. (Three predicate adjectives.)
In her will, the woman left jewelry, coins, stocks and bonds, but no cash. (Four direct objects of the transitive verb left.)
The director, the assistant chief, and the chairperson held a confidential meeting. (Three subjects.)
Neither the president, the vice-president, nor the chief financial officer may authorize this particular capital expense. (Three subjects.)
The personnel committee reconsidered this issue, found that the supervisor had exceeded her authority, and granted the relief requested by the employee. (Three predicate verbs.)