Take a look at the following link for tips on critiquing: http://www.blehert.com/essays/critique.html
In particular, pay attention to this paragraph: “Critiquing others well improves an artist’s work: A good poetry critic reads the poem intelligently, notes his own response to it AND what in the poem caused that response. Also, using that same ability to duplicate the viewpoints of others, the critic understands the response INTENDED. For example, even though unmoved by a poem, he can sense (if he’s a good critic) that the author intended him to be moved in a particular way.”
Finally, take a good look at the section entitled “Guidelines for Critics”.