Everyone's work, even if it is wrong, is thought of by others. As long as you work hard, it must be valuable to him. Pointing out other people's mistakes directly without reservation and without turning is tantamount to directly denying other people's efforts. Therefore, the best way to point out a person's mistakes is to affirm his behavior and thinking first, and then tell him that you may not be particularly effective. Let's change our thinking. Also, try to use less words like "error" and more words like "I think this is better".
One more thing, when pointing out other people's mistakes, we should have a result-oriented thinking.
The so-called result-oriented thinking is to tell your friends how much loss your mistakes will cause if you follow this practice. Telling each other the possible consequences will make them seriously consider your suggestion and reflect on their mistakes.