What Is Subject-Verb Agreement?
In English, subject-verb agreement is important. What this means is that the characteristics of the subject should be reflected in the verb. For example, if a subject is singular, the verb form must also be singular.
Plural and Singular Subject
In the present tense, nouns and verbs agree in opposite ways. When the subject is plural usually and “S” to show that it’s plural. 
Example subjects :
Car → Cars.
ΓÇ£The cars look expensiveΓÇ¥ (Plural).
ΓÇ£The car looks expensiveΓÇ¥ (Singular).
Baby → Babies.
I, you → Plural subjects.
He, she, it → Singular subjects.
Auxiliary Verb
Do/does → In the present simple.
Am/is/are/was/were → In the continuous tenses.
Have/has → In the perfect tenses.
To think about the subject-verb agreement because the auxiliary verb, because the agreeing verb, the verb that agrees with the subject.
Example :
The dogs donΓÇÖt want it.
The dog doesnΓÇÖt want it.
We are going to the beach.
He is going to the beach.
Modal Verb
May
Could
Will
Must
Should
They help the main verb in the sentence but the subject-verb agreement rules are different with modal auxiliary verb. The verb following a modal verb is never in the ΓÇ£SΓÇ¥ form. ItΓÇÖs always in the infinitive form.
Example :
My friends might come.
My friend might come.
Indefinite Pronoun
Everybody
Nobody
Anybody
Someone
Usually indefinite pronoun take singular verb.
Example :
Everybody wants to be loved.
Nobody likes to be left out.
Compound Subjects
Group nouns and relative clauses.
Example :
My Mum is happy for me.
My Mum and Dad die proud of me.
Subject and subject
              +
     Plural verb
Example :
Peter or Paul is coming.
Peter or Paul are coming.
Group Nouns
Single nouns that are actually groups of people or things.
Club
Team
Company
Family
Crowd
Class
Example :
The team is organising the event.