Being the target of a critiquing session for writers is like how most people react to going to the dentist's office: Both involve being stuck in a chair and forcing yourself to endure, well, often less-than-pleasant attention from the hands of people, who tell you what to being doing better, be it flossing or good pacing in dialogue. Word Nerd isn't sure how dentists react all the time to people who want to flee their offices, but being on the giving end of critiquing isn't always a whole lot of fun either.
Critiquing is tough. Bottom line. No writer wants to hear only, "I like it." That's no help. Of course, neither does a writer really want to come back from a critique session feeling like it was a scene out of a slasher movie, with a manuscript given back hacked up and dripping with red ink.
So what's a critique-er to do? Apply the golden rule -- critique others the way you would want to be critiqued. Give thoughtful, insightful comments about places that need work. And don't forget to mark the good stuff to let the author know the places you laughed outloud or caught foreshadowing or whatnot. If the piece isn't a genre you're really familiar with, that makes it tougher sometimes to stick with it. That said though, every story needs well developed characters, good dialogue and rising and falling action. As a critiquer you can look for those elements in any story. The more you give critiques, the better you get at it, and the more it can help you identify trouble spots in your own writing before you ever put it up for critique.
Sometimes though critiquing still ends up like flossing: you just have to do it.