• When mailing or posting chapters or scenes, explain to the critiquers what you'd like help with--i.e. "Is the overall emotional content of the work consistent?"; "Does the dialogue achieve what I want it to?"; "Don't worry about the grammar, I know I need to work on that."; "Do a line by line critique."; "Focus only on content."; etc.

• When critiquing, start and end with the positive aspects of the work being critiqued.

• Mail or post second draft material, so less time is spent on correcting basic
  technique.

• Be polite and professional! Remember, this is a business.

• Think before you speak! (Or write, as the case may be.) There are ways to word your comments to soften a blow and give helpful suggestions.

• It's always good practice to thank people for critiquing your work.

• Always keep in mind that your work is your own. Critiques are given only as suggestions for improvement. As the author, you decide what suggestions or advice to follow. You know what would work best for your writing.

UNACCEPTABLE BEHAVIOR IN CRITIQUING

• Destructive criticism. Try not to offend the author by starting comments with: "I don't like it/him/her." The purpose of a critique is to see the author's vision and help them achieve it.

• Trying to change someone else's story or style to suit your own likes.
  Respect differences in writing styles.

• Hammering home your point. Say it once, and then leave the decision of
  whether to take the suggestion onboard up to the owner of the work.

• Words/phrases such as: "That's stupid"; "No one would do that"; "He's a
  jerk/She's a bitch"; "I can't stand xyz"; etc.

• Putting down others' works to make yourself feel better.

• Sarcasm. Even if you're friends with another reader, saying "She'll know
  I'm just kidding" is not acceptable. Everyone is very close to their work,
  and that makes them vulnerable.

• Critique wars: no arguments between critiquers over a third person's work.
  It wastes time and takes the focus off helping.

• Keep personal taste out of critiques. Just because you don't read
  vampires/baby/angel/paranormal books doesn't mean you can't give
  constructive comment on the manuscript in question.

Finally, if you get upset by a critique, take some responsibility in sorting out the situation. Sometimes people aren't aware they're being abrasive, and sometimes you're taking things a little too seriously. Try to resolve differences first but if you can't work it out, you have the prerogative of asking the person to not critique your work in future. This should be your last alternative. Always keep in mind that critique groups or partners are there to give and receive support.