Rule 1: Use a singular verb form (a verb ending in –s) if your subject is a he, she, or it. Singular subjects include, but are not limited to, these:
Singular nouns: A list of phone numbers is available. A major problem is smokers.
Singular indefinite pronouns: Each of us has a key.
Subjects preceded by each, every, or many a: Every Tom, Dick, and Harriet has an opinion.
Subjects preceded by the number of: The number of students attending college is very high.
Titles/names of companies, books, plays, movies, etc.: The Centers for Disease Control is in Atlanta, Georgia.
Gerunds: Recycling telephone directories helps save landfill space each year.
Relative pronouns referring to singular antecedents: Ora is the only one in the group who smokes.
Subjects joined by or, nor, either…or, or neither…nor: Neither the players nor the coach was present.
Nouns plural in form but singular in meaning: Measles is a childhood disease.

Rule 2: Use a plural verb form (a verb that does not end in –s) if your subject is a they. Plural subjects include, but are not limited to, these:
Subjects joined by or, nor, either…or, or neither…nor: Neither the coach nor the players were present.
Plural indefinite pronouns: Both of us have a key.
Plural nouns: The scissors are lying on the desk.
Subjects preceded by a number of: A number of students are majoring in law.
Relative pronouns referring to plural antecedents: He is one of the millions of people who smoke.

Rule 3:
Ignore prepositional phrases: A list of phone numbers is available.
The governor, along with his advisers, has already left.
Ignore there and here at the beginning of a sentence: There are three books on the censored list.
Ignore appositives: They each have a ticket.
Ignore words synonymous with the subject: Clothes are her passion.
Her passion is clothes.

Rule 4:
Some subjects may be singular or plural depending on the meaning of the subject.
Some of the food is cold.
Some of the vegetables are cold.
The cast was congratulated. The cast were practicing their lines.
Fifteen minutes is a long time. Fifteen minutes remain.
Statistics is a difficult course. Divorce statistics are alarmingly high.