The bottom line is that work has to come first, before group identity or friendship or ego. That doesn't mean a critique has to be unkind, simply that it has to be honest.

An honest critique requires introspection on the part of the critic. I have to be aware of my own tastes and prejudices, and to be able to present my reactions to the work as personal. That's tougher than it sounds.

A critic needs a thick skin just as much as an author. It's easy to say "this sux bawls!" It's much harder to say, "I was confused at this point, angry about what happened to that character, and disappointed when this other thing didn't happen."

A good critique means being vulnerable. It means telling a writer, "this is how you made me feel."