Objectivity is crucial to constructive criticism.The goal is to communicate that a performance standard has not been met. Your sentiments/judgments are irrelevant.

Deal in facts

When preparing to tell someone what they did wrong, avoid using qualifications like "With all due respect," "No offense," or "Don't take this the wrong way" to soften criticism.

Never qualify

Criticism without an action plan is worthless. Give people direction or keep your mouth shut.

Show them the way

If people feel you support their fundamental views and value them, the change will be easy and natural.

Let the fixes feel like their own

... when telling someone they're wrong.Be concrete and don't sermonize, even if the person that's receiving your criticism knows she did something wrong.

Ambiguity is your enemy

... and if you must amplify your message, say where your data came from. Never try to simultaneously be a good cop and a bad cop. Make it clear that your goal is constructive change.

Say what the problem is

For example, in saying "You were lazy in preparing this report" you may think you are helping the other person to improve a skills; instead, it addresses your assumption about the person's attitude toward their work.

Focus on behavior, not character

There are plenty of reasons not to tell someone they're wrong. It's uncomfortable, for one thing. You also might come off as rigid, unsympathetic, arrogant, or worst of all, politically incorrect. In some cases, depending on how much alcohol is involved, you might even get smacked in the mouth.

Focus on behavior, not character

Similar ideas to Focus on behavior, not character

focus on results

2. Focus On The Situation, Not The Person

Remind both parties that they are on the same team