All critique photographs, whether they are their own or those of other people.
Here's a few things they look at and make money while they're doing it--
2. Following the Rule of Thirds.
3. Exposure--no white outs or black outs.
4. Depth, perhaps using natural elements such as mist or smoke to add depth.
5. Perspective, there's noting like having your viewers eyes look down a railroad.
6. Light, light is everything. Scatter it. Beam it. Churn it. Twirl it.