First of all, you will need to find a common thread between the two stories. For example, you might say that both of them demonstrate the conflict between dreams and reality, or the loss of hope. Then, you describe how the authors use characterization, mood and symbolism to explore the theme in each story.
Once you have your thesis, I would choose to write a paragraph for each of the elements you listed. For example, your first main point paragraph would be about how the author uses characterization to explore the concept of __________________ (whatever your thesis is related to dreams and reality). For example, you might say that one character is hopeful and another is pessimistic. Explore their character traits, and how the authors use those traits to explore the theme.
Then, your second paragraph would do the same thing with mood. How does the atmosphere of the two stories compare? How does the atmosphere relate to dreams? Is one story more realistic to you?
Finally, choose important symbols from both stories that mean the same thing or something related. It might even be the same or a similar symbol. Explore how the author uses it to relate to your thesis statement about reality and dreams.