Despite using 'no offence', your tone can still convey rudeness. Be genuine in your delivery. 'No offence, I think you could have handled that better.' said with a concerned tone.
Pro Tip 2/3
Still Offensive
'No offence' doesn't guarantee the other person won't be hurt. Use it carefully. No offence, some people might still find your comment hurtful.
Pro Tip 3/3
Colloquial Use
Mostly used in casual conversations, might be inappropriate in formal settings. 'No offence, but that idea just won't work.' - might not be suitable for a business meeting.