Definition:
Subject/Verb Agreement tells the writer in which instances a singular or plural verb should be used.
[http://owl.english.purdue.edu/owl/resource/599/01/]
When to use it:
You should:
-Subject/Verb Agreement should be used at all times, making sure that a group of students is not doing the action of a singular person.
-There are some exceptions to the rule that I will mention later.
How can it help:
-Subject/Verb Agreement can help you understand who and how many are doing what actions.
Ex:The man, accompanied by his wife, is due in California in four days.
(This sentence helps the reader understand who is the main subject by noticing it is a singular action even though two people were mentioned.
Correct Usage:
-With 'subject AND subject' use the plural version of the verb.
-With 'subject OR subject' use the singular version of the verb. Also in the case of 'NOR'
-With 'plural subject OR singular subject' use the singular subject because it would be closer to the verb assuming that the Plural Subject is the start of the sentence.
-Collective Nouns should be use the singular version of verbs even though they reference more than one person.
Ex:The boy and the dogs are all going to be going to the Emmy's on Sunday.
Ex:The boy or the girl is in the closet.
Incorrect Usage:
-Single objects with more than one part should have a plural verb.
Ex:The boy and the dogs is all going to be going to the Emmy's on Sunday
Ex:Michael Jackson or Lady Gaga are in the closet.