Appraisal, feedback and evaluation help polish a written piece. We all appreciate an honest assessment of our work, but no one wants a scathing criticism. Here are some ideas regarding feedback:
Read (or listen) carefully. Be honest in letting the writer know how the piece made you feel. If you are unfamiliar with, or don't like, that particular style or genre, let the writer know. Then give examples of what worked for you, and what didn't. Give specific suggestions as to which words or phrases could be changed to improve the clarity, atmosphere etc. Be gentle, since the writer may never have shown their work to anyone else.
When you receive feedback, note the main points. If you have questions, ask for clarification, but don't argue. We all have different preferences. Thank others for their comments. You don't have to incorporate everyone's opinion when reviewing your work,