Common grammatical mistakes writers, including myself, are prone to making:
1.When the subject of a sentence is composed of two or more nouns or pronouns connected by and, use a plural verb.
Eg. She and her friends are at the fair.
2. When two or more singular nouns or pronouns are connected by or or nor, use a singular verb.
Eg. The book or the pen is in the drawer.
5. Do not be misled by a phrase that comes between the subject and the verb. The verb agrees with the subject, not with a noun or pronoun in the phrase.
7. Nouns such as civics, mathematics, dollars, measles, and news require singular verbs.
8. Nouns such as scissors, tweezers, trousers, and shears require plural verbs. (There are two parts to these things.)
10. Collective nouns are words that imply more than one person but that are considered singular and take a singular verb, such as: group, team, committee, class, and family.
In very few cases, the plural verb is used if the individuals in the group are thought of and specifically referred to.
Example of the Exception:
My family have never been able to agree. (correct)
My family has never been able to agree. (wrong)