A collective noun takes a singular verb and a single pronoun when the collection is thought of as a whole.

E.g The board decides who will be the next CEO & its decision is irrevocable.

#When an abstract noun is used as a collective noun, the verb should be in plural form

E.g The youth are building block of their nation

Youth is an abstract noun that is the reason we have used "their"

#If two singular nouns refer to the same person or thing, the verb must be in singular form.

Incorrect-The founder and President are coming.
Correct- The Founder and The President is coming.

#Each is used in speaking of two or more things and every is used only in speaking of more than two.

Incorrect-There were only two soldiers but every soldier is equal to five policemen.
Correct-There were only two soldiers but each soldier was equal to five policemen.

#We use the article with holy books, continents, oceans, rivers, planets and seven wonders of the world.

#Use a singular verb with distances, period of time, sums of money etc when considered as a unit.

E.g Three miles is too far to walk.

#When two or more singular nouns joined by 'or' or 'nor','either....or','neither....nor',the pronoun used for them should be in the singular.

E.g Neither Rakesh nor Raju has done his homework.

#When two or more singular nouns are joined by 'and' the pronoun used for them must be plural.

Incorrect-Both Ram and Shyam have done his homework.
Correct- Both Ram and Shyam have done their homework.

#Two conjunctions should not be used in the same sentence.

Incorrect-Although she was tired, but she still went on working.
Correct-Although she was tired, she still went on working.

#Use the possessive case with gerunds.

E.g All child safety seats must be properly installed to reduce the risk of a child's being injured