Wrong Conditional Perfect Tense

When talking about something that didn’t happen in the past, many people (including me ;-)) use the conditional perfect (if I would have done) when they should be using the past perfect (if I had done).
For example, you find out that your brother saw a movie yesterday. You would have liked to see it too, but you hadn’t known he was going. To express this, you can use an if - then clause. The correct way to say this is with the past perfect in the “if” clause, and the conditional perfect in the “then” clause:
Correct: If I had known you were going to the movies, [then] I would have gone too.
The conditional perfect can only go in the “then” clause — it is grammatically incorrect to use the conditional perfect in the “if” clause:
Incorrect: If I would have known you were going to the movies, I would have gone too.

More examples:
Correct: If I had gotten paid, we could have traveled together.
Incorrect: If I would have gotten paid, we could have traveled together.
Correct: If you had asked me, I could have helped you.
Incorrect: If you would have asked me, I could have helped you.
The same mistake occurs with the verb “wish.” You can’t use the conditional perfect when wishing something had happened; you again need the past perfect.
Correct: I wish I had known.
Incorrect: I wish I would have known.
Correct: I wish you had told me.
Incorrect: I wish you would have told me.
Correct: We wish they had been honest.
Incorrect: We wish they would have been honest.