Ambiguity is your enemy

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.

• Determine whether the person you’re talking to is open to receiving your advice. Is she literally asking for it? 
• If there’s no concrete question, assess her body language. Is she leaning into your conversation, does she seem engaged, eager to hear what you ...

When telling someone he's wrong, don't be too direct with your approach:

Before jumping right in with something like, “This is really wrong!”, try saying, “It’s evident that you put a ton of time and effort into this project, and it looks great!”