Here are some examples of the mistakes certain "types" of critiquing creatures will make. Learn from them!
1. The Vampire
He's a parasite, feeding off the hard work, sweat, and yes, blood of others. He wants to take, take, take, but forgets to give. He scribbles a quick, nice job on the top of your pages, but expects a line by line critique from you. He needs to learn to give because not only is it the RIGHT THING TO DO, to hold up his side of the bargain, but it's also helpful to him. Because when he's looking at what works and doesn't in your writing, he'll learn what to look for in his own.
2. The Ghost
She's not really there. Whether physically or emotionally. She refuses to open up and really share. Nor is she open to criticism. She's defensive and doesn't want to hear it. Well, guess what? She's not going to get anything out of the group! If you can't open yourself to finding the flaws in your own work, you'll never grow. And that's just sad.
3. The Werewolf
She attacks, going right for the jugular. She won't pull any punches. And at first glance this may seem the right way to go. But that's the last thing to do if you want anyone to hear what you're really saying. There are delicate ways to approach these things. Ever hear of the sandwich method? I know, I know, werewolves aren't known for liking sandwiches, but that's the problem! Study it if you don't know it.
4. The Fairy
He (let's not be sexist here people) is too sensitive and doesn't want to hurt your feelings. So he won't be honest. That's not doing anyone any good. Yes it's nice to hear "It was incredible!" But how does that help your revision? He could also benefit from learning the sandwich method. He needs to understand that by giving specific feedback, he's actually being the best friend of all.
Have you met any of these creatures? I hope they aren't in your critique group! If you haven't found one, keep searching. Because feedback is so very important. It's impossible for you to see everything. And sometimes it's right below the surface until someone else says it and you have one of those AHA moments, which are wonderful.