OPTIC. I find Walter Pauk’s theory quite useful when writing about an image. The AP Art History Course also uses this Acronym as a successful approach to writing about visual art. I have adapted it here with further commentary and explanation in light of your specific goals.
The point of the first two steps is pure description. What does your eye notice first? Then what? Think space, color, dimension, etc...Notice what you notice. You are doing this so that explicating will be easier and better. Pick and image that you can describe with words.
- Overview: Conduct an Overview of the visual or graphic. I recommend an extensive brainstorming process here.
- Parts: Key in on the Parts of the visual by noting any elements or details that seem important. The old cliché goes “a picture is worth a thousand words”, which translates to about three pages. I think this is a good rule of thumb, but by no means a fixed rule. Describe what you see. Where do your eyes go to first? Then what? Follow the natural progress of where your eyes go. Give as much detail as possible.
- Title: Explain the Title (if one is present) and its relation to the piece of art. Even an “untitled piece” may tell you about the artist’s aesthetic.
- Interrelationships: Use the title, or your theory, and the parts of the visual as your clues to detect and specify the Interrelationships in the graphic. In other words, this is where you develop your thesis about the image and connect ideas.
- Conclusion: Draw a Conclusion about the piece as a whole.
 Pauk, Walter. How to Study in College. Boston: Houghton Mifflin, 1997, 271.