One easy way to make sure that subjects and verbs agree in number is to apply the "opposite rule." In present tense sentence constructions, singular subjects don't end with an "s," while singular verbs usually end with an "s." On the other hand, plural subjects end with an "s," while plural verbs don't end with an "s." For example, the following sentences display the "opposite rule" and are singular and plural, respectively:
1. The student walks to class. (Singular)
2. The students walk to class. (Plural)
Content that comes in between the subject and the verb can make subject-verb agreement tricky. One type of construction that can come between a subject and a verb is a prepositional phrase. For example, a sentence like "The number of students is increasing" includes the prepositional phrase "of students." This is tricky because "number" is the subject and is singular, but "students" is plural. Therefore, you may be tempted to use a plural verb form like "are." Furthermore, the word "students" is located closer to the verb. One way to ensure that you have the correct subject-verb agreement is to ignore the prepositional phrase before matching the subject and verb.
Clauses that begin with "who," "that" or "which" can be tricky in subject-verb agreement. These phrases separate the subject from the verb, much like prepositional phrases do. For example, a sentence like "Anyone who rides on trains is conscious of the environment" has a relative clause. To make sure the subject, "Anyone," agrees with the verb "is," you should ignore the relative clause.