For the outline of the prompt, determine your characters, setting, and main focus.
Characters can be anyone you'd like, as long as they are a slave. The setting could be a slave state like Florida or Arkansas in the 1860s. The main focus is what it was like being a slave. Use the resources listed below to study the thoughts and emotions of slaves, and then write from a similar point of view.
http://www.ushistory.org/us/27b.asp
http://blackloyalist.com/cdc/story/revolution/slavery.htm
http://www.eyewitnesstohistory.com/slavelife.htm
http://www.digitalhistory.uh.edu/disp_textbook.cfm?smtID=2&psid=3040
Good luck!