The petals of the rose should be well hydrated (turgid to the touch, not limp) and should be free of any brown spots or discoloration.  Look for petals that do not have any creases or physical damage.  The foliage of the rose should not be stripped completely from the stem and should be free of pesticide residue.  The petals of the rose should still be tight and in a bud form with a slight amount of opening.