“The opposite of love is not hate, it's indifference. The opposite of art is not ugliness, it's indifference. The opposite of faith is not heresy, it's indifference. And the opposite of life is not death, it's indifference.”
This is a great Elie Wiesel quote (first heard by me in a Lumineers song). I think if one is viewing art in a form they aren't accustomed to - i.e. almost everybody's experience reading poetry, even some people who write it - then the best way to gauge whether it's "good" or not is 1) how much it "grabs" you (catches your attention and holds it), or, the other end of the spectrum, 2) how much it leaves you indifferent to it, that is, how little your mind returns to it, or how quickly it discards the sensory data (information, art object) and moves on to something different.
So my advice to novice audience-members of any art form is - just go with the flow; experience the art. If you can't escape it afterward, if it resides in your mind after you're no longer viewing it, it's 'subjectively' (you being the subject) "good"; if you forget about it, it was "bad."
What irks me is hearing other poetry writers / readers laud every poem they see...not EVERY poem they see, not the poems people they know have written, but the poems on websites or in books or journals, because they assume some authority has deemed it a "good poem" and that they, the readers, aren't good enough yet to tell what is good on their own. It took me a couple years to learn there is no such thing as an objectively good poem; the poems that live on are considered "good" by a vocal and powerful few, and then are accepted as good by the unwitting or naive majority (namely college students or retirees). Fortunately, if you stay with poetry, you'll see some of these vocal and powerful few were actually right, or their tastes agree with yours (I often find myself agreeing with Bloom on matters of aesthetics; if I were a critic I'd champion Crane, Stevens, Ashbery and Dickinson, too), but first you have to stop thinking everything is great. Poetry is like TV, Hollywood movies, pop music - 99.9% of it is CRAP. (See Sturgeon's Law.)
For me, what's attention grabbing is still what's new, so I think the only critic who's ever remained valuable to me is Pound; fascist, anti-semitic Pound. If you want to know how to read, read http://www.amazon.com/ABC-Reading-New-Directions-Paperbook/dp/0811218937