Having yourself or a second party evaluate your photographs is an important and constructive step in developing your craft. If your purpose for taking photos is to exhibit them to the public you will surely reach this step almost immediately. A proper critique for a photograph usually focuses on 5 main aspects of the photo: content, background, technical, craftsmanship, and finally your general feelings on the photo.
First look at the composition or content in the photograph. What is the center of interest in the picture? Where did the photographer place it in the frame? Did the photographer get close enough to the subject to include only what is important, or are there wasted parts of the picture with elements that do not add to the message of the photo?
Next, observe the background in the photograph. How did the photographer represent the background in regards to focus and depth of field? How does the background add or distract from the message of the photo?
Now take a look at the technical camera work involved in the photograph. Is the subjects sharp and clearly in focus? Is the photo exposed properly? A properly exposed photo will have some texture in the shadows. Are details missing because of over or under exposure?
Then look at the craftsmanship the photographer exhibits. Does the physical photo have spots, stains, or scratches? Is it placed nicely in a frame or elaborately displayed? Is there evidence that the photograph was made with care in the process?
Finally, offer your own personal feelings on the photograph. What do you like about the selected subject? Is it an emotional shot, a story, a statement, a humorous photo? What would you do differently if you had the chance to take the same photograph?
Collecting the opinions and critiques of unbiased second parties is crucial to develop better communication in your photos, but it is also just as important to critique your own photos. Discover what it is you like or dislike about your art and expound on it.