Subject-Verb Agreement Rule:

 Singular subjects require singular verbs.

Plural subjects require plural verbs.

Beware of:

 1.   Prepositional phrases between subjects and verbs

Subjects and verbs are never within prepositional phrases.

2.  Compound subjects

Two subjects linked by the conjunction "and" require a plural verb.

3.  Collective nouns as subjects are considered singular and take singular verbs.

4. Either/or and Neither/nor situations

Either means one of two, so either usually takes the singular form of the verb.

In an either/or or neither/nor situation, the verb agrees with the closer subject.

Informal writing rules allow the use of the plural form of the verb: Have either of you bought your tickets for the movie?

5.   Indefinite pronouns as subjects

Singular indefinite pronouns: anybody, anyone, anything, each, either, everybody, everyone, neither, nobody, no one, one

Plural indefinite pronouns:

6.   Here or There as the beginning word of the sentence

Here or There is never a subject. Find the subject after the verb.

7.  Plural noun specifying a singular quantity