Do not use they to refer indefinitely to persons who have not been specifically mentioned. If you use the pronoun they, it should refer to a specific antecedent.
The word it should not be used indefinitely in constructions such as the following.
The pronoun you is appropriate when the writer is addressing the reader directly:
Except in very informal contexts, however, the indefinite you (meaning “anyone in general”) is inappropriate.
The writer could have replaced you with one, but in American English the pronoun one can seem stilted.
Exercises:
Pronoun reference 1
Pronoun reference 2
Pronoun reference 3
Pronoun reference 4