Feedback should be about behavior not personality.
Do: “You spoke so quietly I couldn't hear.”
Don't: “You shouldn’t be so shy.”
Feedback should describe the effect of the person’s behavior on you.
Do: “Your props helped me understand.”
Don't: “We all loved the props.”
Feedback should be as specific as possible.
Do: “Your presentation helped me see a problem I didn’t know existed.”
Don't: “I liked the presentation. You did well.”
Feedback should be timely.
Do: “Your presentation on rocks was thorough today.”
Don't: “Last time, I couldn’t hear you.”
Read more at: https://www.skillsyouneed.com/ips/feedback.html