The verb must agree with the subject, not with other nouns that come between. Be particularly wary of prepositional phrases:

THE WHEELS OF THE BIKE WERE BENT IN TRANSIT.

The prepositions as well as, in addition to, together with, and along with prove particularly troublesome. Do not change the singular verb to plural:

TIM AS WELL AS MICHAEL WAS CONFUSED BY THIS LESSON>

Most compound subjects connected by and are treated as plural:

SYDNEY AND LAURA ARE DOING WELL WITH PUNCTUATION.
Exception: when the parts of a subject form a single unit or when they refer to the same person or thing, treat the subject as singular:

PEACHES AND CREAM WAS THE DESSERT SERVED AT LUNCH.

When a compound subject is preceded by each or every, it is treated as singular:

EACH MAN, WOMAN, AND CHILD IS TREATED EQUALLY.
Exception: when each follows a compound subject:
TRACY AND JOHN EACH HAVE A LOT TO SAY.

Compound subjects connected by or or nor, or by either. . . or or neither. . .nor, make the verbs agree with the part of the subject nearer to the verb:

A SKIRT OR JEANS ARE ACCEPTABLE TO WEAR.
NEITHER A ROSE NOR FERNS ARE AVAILABLE.
Hint: it is less awkward to keep the plural subject last.

Most indefinite pronouns (pronouns that do not refer to specific persons or things: any, anyone, everybody, each, either, everyone, everybody, everything, neither, none, no one, someone, something) are treated as singular:

EVERYONE WHO SIGNED UP WAS GIVEN A PRIZE.
Exception: when none or neither is followed by prepositional phrases with a plural meaning, usage varies. It is safest to treat them as singular:

NONE OF THESE SENTENCES WAS ACCEPTABLE.

Collective nouns are treated as singular inless the meaning is clearly plural.
Hint: the group is treated as a singular unit inless there is a reason to draw attention to the individual members of the group:

THE FAMILY IS IN AGREEMENT ON THIS MATTER.

Make the verb agree with its singular subject even when the subject follows the verb.
Hint: this usually occurs when starting sentences with there is or there are:

THERE WAS A SMALL DOG IN THE ROAD.

Make the verb agree with its subject, not with a subject complement (a subject complement names or describes the subject):

A FORK AND A KNIFE ARE CONSIDERED EATING UTENSILS.

Who, which, and that take verbs that agree with their antecedents (or the nouns or pronouns to which they refer).

THE JANITOR WHO WORKS THE EVENING SHIFT WAS LATE AGAIN.
Watch constructions, however:

ONE OF THE JANITORS WHO WORK THE EVENING SHIFT WAS LATE AGAIN. (PLURAL)

ONLY ONE OF THE JANITORS WHO WORKED THE EVENING SHIFT WAS LATE AGAIN. (SINGULAR)

Words such as athletics, economics, mathematics, physics, statistics, measles, mumps, and news are usually singular, despite their plural form:

MEASLES IS DANGEROUS IN PREGNANCY
Exception: these words are considered plural when they describe separate items rather than a collective body of knowledge.

THE STATISTICS ON AIDS ARE FRIGHTENING.

Titles of works and words mentioned as words are singular:

THE TOMMYKNOCKERS WAS WRITTEN BY STEPHEN KING.

To express the subjunctive mood (a situation or condition that is untrue, not yet true, or highly unlikely), use were instead of was. The subjunctive is indicated by the words if, as if, as though, or wish:

IF I WERE YOU, I WOULD REWRITE THE WHOLE PAPER.
I WISH MY INSTRUCTOR WERE AMENABLE TO BRIBES.
Exception: use was if the situation following if, as if, or as though could be true:

I FELT AS THOUGH I WAS GETTING BETTER AT SUBJECT/VERB AGREEMENT.

A number used as a subject requires a plural verb; the number used as a subject requires a singular verb. Keep in mind that descriptive adverbs and adjectives may separate the article a or the from the word number:

A NUMBER OF VACATION DAYS HAVE ALREADY PASSED.
THE NUMBER OF VACATION DAYS HAS DECREASED.

Avoid splitting an infinitive; that is, avoid placing any words between to and the verb form:

WERE YOU ALL ABLE TO COMPREHEND FULLY THE CONSEQUENCE OF COMMITTING THE CRIME?

A relative pronoun clause must agree in gender and number with the noun or pronoun it modifies:

OUR TEACHER IS THE KIND OF MAN WHO IS ALWAYS RESPECTFUL OF HIS STUDENTS.

Relative pronoun clauses preceded by such phrases as one of those agree with the plural noun and therefore must take a plural verb:

SHE IS ONE OF THOSE STUDENTS WHO DAILY DO THEIR STUDIES.