Incorrect: Both did not come.
Correct: Neither came.

Incorrect: Both of them did not pass the test.
Correct: Neither of them passed the test.

In negative clauses, we use ‘neither’ not both.

Incorrect: Each of these girls sing very well.
Correct: Each of these girls sings very well.

After each and every, we use a singular verb.

Incorrect: We all did not go.
Correct: None of us went.

Incorrect: We all had not been invited.
Correct: None of us had been invited.

Incorrect: One should love his country.
Correct: One should love one’s country.

Incorrect: ‘Have you got a pencil?’ ‘No, I haven’t got.’
Correct: ‘Have you got a pencil?’ ‘No, I haven’t got one.’ / ‘No, I don’t have one’.

Have is a transitive verb. It needs an object to complete its meaning.

Incorrect: ‘Is he at home?’ ‘Yes, I think.’
Correct: ‘Is he at home?’ ‘Yes, I think so.’

Incorrect: We enjoyed during the holidays.
Correct: We enjoyed ourselves during the holidays.

Enjoy is a transitive verb. It requires an object.

Incorrect: The boy who works hard he will get the prize.
Correct: The boy who works hard will get the prize.
Correct: Whoever works hard will get the prize.

The relative pronoun serves as the subject of the verb in the relative clause. It is therefore wrong to write another subject.