Feedback

Useful rather than comfortable.

Structure

Name the specific behaviour, the effect it had, and what to do instead. Vague praise and vague criticism are equally useless.

Feedback about work, not about character.
Ask before giving unsolicited feedback; timing matters as much as content.

Receiving it

Listen, ask for an example, and thank the person before defending anything. People stop giving feedback to those who argue with it, which removes your best source of information.