There's no easy way of answering that on this kind of medium (an Internet forum). I took two graduate seminars and wrote several papers on it :) But as a primer, I strongly suggest reading Hume's 'Of the standard of taste': http://www.econlib.org/library/LFBooks/Hume/hmMPL23.html
In that essay, he attempts to provide some clear-cut criteria for an objective judgment of art, food, and literature.
(Note that there ARE people that are relativists and they have a somewhat compelling argument. That's perfectly fine. I just don't buy it and I think they're wrong.)