1.if two or more singular noun joined by and are used in a sentence,the pronoun instead of these nouns will be plural.i.e.
John and Bony are learning their lessons.
2.if there are each or every before two singular nouns joined by and,the pronoun instead of them will be singular.i.e.
Every clerk and every peon must do his duty.
3.if two or more nouns are joined by either. . . .or/neither. . . . nor,the pronoun instead of them will be singular.i.e.
Either Rahim or Karim did his duty.
Neither Rana or Kamal will try his best.
4.if a plural noun and a singular noun are joined by or/nor,the pronoun will be plural.i.e.
Either the teachers or the headmaster succeeded in their attempt.
5.the pronoun used in lieu of any collective noun is in singular number and neuter gender and the verb is singular also.i.e.
The jury was divided in its opinion.
But the pronoun instead of noun of multitude is plural and the verb are also plural.i.e.
The jury were divided in their opinion.
6.the number ,gender and person of any pronoun will be as the same of the noun instead of which it is used.i.e.
The lady lost her purse.
He is a poet.
7.if there are first person,second person and third person in a sentence,one has to put second person at first,third person after that and next first.it is called in short 231.i.e.
You,he and I are friends.
8.if first person is used with other noun and pronoun ,the pronoun which is used instead of them will be first person.The pronoun which is used instead of second person and other noun ,pronoun will be second person.For third person,the pronoun will be third person.i.e.
He and I did our duty.
You and he did your duty.
She and her friends did their duty.