Are you looking for topics to focus on? If so, one of the main themes of the novel is the tension that exists between races. Another theme that you could write about would be imperialism. Conrad especially focuses on how imperialism creates greed and ruthless selfishness. A possible analysis you could do would be a historical analysis of imperialism and how it is represented in Heart of Darkness. If you are looking for something that is central to the book, you could write on the effects of imperialism on race relations as represented by Conrad. I hope that gives you a few ideas to run with.