In reference to critiques, I use the four basic steps and explain them thoroughly:
Describe- list the basic objects, shapes, colors, lines, etc. This usually covers the elements of art
Analyze- discuss the relationships of the objects, etc., to each other. anything repeated? similar? this usually covers the principles of design
Interpret- what do you think it means? does it evoke any feelings? what's happening in the image?
Judge- do you think it is a successful work of art? why or why not? do you personally "like" it? why or why not?
I did a class critique of an abstract work by Picasso. I thought it was very successful because of the questions that I used to prompt some substantial answers. I had them write their thoughts for each step first and then discussed it with the class. Then they did group or individual critiques.