You aren’t casting judgment on a work, you’re coaching the writer. Remember to include the writer in the process, helping them find the draft’s strengths and weaknesses rather than telling them what they are or are not doing wrong.
Check with the writer to make sure you’re understanding the main ideas of the work.
Give specific compliments as well as specific criticism; reviewing isn’t just about one or the other.
If you find a passage confusing, ask the writer for clarification.
Always express an interest in reading the next draft.