Before you settle on a topic, do a little preliminary research. If you are not very familiar with your topic, get some information on it from a general reference source, such as an encyclopedia. This will introduce you to the various aspects of your topic. Some good online library resources to try are Encyclopaedia Britannica, Credo Reference, and Gale Virtual Reference Library.
Also, take the time to do a quick search of the library's online catalog and journal databases. This will help you to see if references are readily available on your topic. Nothing is more frustrating than choosing a topic, then discovering that you cannot easily find enough useful information. This will also help you determine if you need to change the focus of your topic by either narrowing it or broadening it.