Incorrect: The boy who works hard he will win.
Correct: The boy who works hard will win.

Explanation

This sentence has two clauses ‘the boy will win’ and ‘who works hard’ and each clause has its own subject. There is no need to use a pronoun when the noun it stands for is already present in the clause.

Incorrect: Whoever does best he will get a prize.
Correct: Whoever does best will get a prize.
Incorrect: Who painted this picture? Myself
Correct: Who painted this picture? I (myself)

Explanation

An emphatic pronoun (e.g. myself, himself, themselves, yourself) cannot be used as the subject of a sentence.

Incorrect: I and he are brothers.
Correct: He and I are brothers.

Explanation

It is considered conceited to put I first when there are two subjects.

Incorrect: I with my friends watched the show.
Correct: I watched the show with my friends.
Incorrect: He himself hurt due to his carelessness.
Correct: He hurt himself due to his carelessness.

Explanation

When a personal pronoun is used as subject it should not be separated from its verb if possible.

Incorrect: He is taller than me.
Correct: He is taller than I (am).

Explanation

The pronoun following than should be in the same case as the pronoun preceding it. Note that this rule is no longer strictly followed and the sentence ‘He is taller than me’ is considered correct.

Incorrect: None of us have seen him.
Correct: None of us has seen him.

Explanation

The words every, each, none etc., are singular in number and should be followed by singular verbs.

Incorrect: People starve when he has no money.
Correct: People starve when they have no money.

Explanation

The noun people is plural in number. The pronoun used instead of a plural noun should be plural in number.

Incorrect: My car is better than my friend.
Correct: My car is better than that of my friend.
Incorrect: The size of the shoe should be the same as this shoe.
Correct: The size of the shoe should be the same as that of this shoe.
Incorrect: His teaching was like Buddha.
Correct: His teaching was like that of Buddha.

Explanation

In a comparative sentence we must be careful to compare the same part of two things. That of, these of and those of are necessary words often omitted by ESL students.

Incorrect: None but I turned up.
Correct: None but me turned up.
Incorrect: They are all wrong but I.
Correct: They are all wrong but me.

Explanation

When but is used as a preposition it means except. The preposition but should be followed by a pronoun in the objective case.