Check if the subject of the sentence is singular or plural. A singular subject refers to one of something, a plural subject to more than one of something. In most instances, a singular subject necessitates a singular verb, a plural subject a plural verb.
Use a plural verb if the sentence contains two singular subjects linked by the word "and." "James and Mary work," for example, where work becomes plural. Were the two singular subjects connected by "or" or "nor," the verb remains singular as the action only relates to one of the persons named. So it would be: "James or Mary works," where works is singular.
Use singular verbs for words such as either, neither, everyone, everybody, anyone, anybody, someone, no one and each. Corporations are also singular, and so require singular verbs: Nike "is" one of the biggest companies in the world -- not Nike "are" one of the biggest companies in the world.
Use a plural verbs when you're a taking about fractions or portions of a plural noun. So it remains -- some of my friends "are" happy, even though you are only referring to part of the plural subject specified. Time and money are always singular.