One of my favorite things about my Writing Workshop class is reading the amazing work of my classmates. One of our directives is to note three things that we love and then we post three questions we have about the pages. I like this approach alot better than picking out something positive then picking out something negative, then ending with something positive.
I don't think it's our place as a critiquer to point out the negative. Is there really a negative? Isn't it really about helping the author produce the best manuscript possible? That's why I like the question approach. Maybe something isn't clear or it didn't come across as the author intended.
For my own critiques, I plan to focus on the similar comments that several people mentioned. Those are the areas that obvious aren't working.
It's interesting that I feel like I'm becoming a better writer by critiquing 70 pages a week. I also love reading the critiques that I'm getting from my classmates and an instructor. I'm always amazed that I have looked at my pages hundreds of times and have not seen something so obvious.
There's such a level of trust in handing over your literary babies and saying "Okay, tear them apart, so I can make them better." It's scary but it's so worth it.
So go out there and find a great critique group.