Do not use the pronoun they to refer indefinitely to persons who have not been specifically mentioned. They should always refer to a specific antecedent.

The word it should not be used indefinitely in constructions such as It is said on television . . . or In the article, it says that. . . .

The pronoun you is appropriate only when the writer is addressing the reader directly: Once you have kneaded the dough, let it rise in a warm place. Except in informal contexts, however, you should not be used to mean “anyone in general.” Use a noun instead.