What is the first thing that must be done when critquing art

The first thing that should be done when critiquing art is to gather information about the artwork.

Explanation:

Critiquing is a method of disciplined, systematic analysis of a written or oral discourse and sometimes it is commonly understood as fault finding and negative judgment. You can give better explanation when you have prior knowledge about the work you are about to critique. However, it can also involved merit recognition, and in the philosophical tradition it also means a methodical practice of doubt.  

typical art criticism goes in this order : describe, analyze, interpret, judgment