Never talk about what you critique to others.
Never show someone else's work to others.
Never "borrow" a critique partner's ideas or characters.
Respect others' time. Critique in a timely manner, and don't send your life's work at once.
Agree upon an amount of work (a chapter or more) and stick to it unless the other person agrees to see more.
Agree on what each of you wants from a critique and give it. Some of the choices are a general overview, copyediting only, or a check on accuracy from an expert.
Be specific. Be fair. Be kind. Don't say, "I hate this." Say, "Your hero is unpleasant because...," or, "He may be rude to the heroine here, but show he is a nice person to others so the reader can like him and see him as a worthy hero."
ALSO mention what works. "The heroine is really charming. I loved the way she...," or "Your descriptions are excellent. I could see the waves around the pirate ship and smell the ocean."
Don't be too kind. If you see a problem, mention it so it can be fixed. It's kinder in the long term for her to know this problem now rather than in the rejection letter from an editor.
Ask questions if you don't understand a comment, but don't defend your work. It's a waste of time for both of you.
Anger is a waste of time, as well. It's no fun to be told that your writing isn't perfect, but you'll have to learn to deal with it. Even the best writers in the world have editors who change things so learn to deal with criticism or forget about a writing career.
Respect each other's voice and individuality. Don't suggest rewrites as you would do it, but rewrites to improve the author's vision.
Respect your own voice and vision. The critiquer can only give SUGGESTIONS. Only you can decide whether to change your work. Only you know what you are trying to achieve with the entire book.
Thank your critiquer because she gave up writing time to help you.
NOTE: Feel free to copy this to share with a critique partner, but if you'd like to share this text otherwise online, please ask my permission. You need not ask permission to link back to this article.