Sources such as encyclopedias and hot topics databases can be good places to get a sense of what some of the areas of interest within your topic are.
Try concept mapping to organize your thoughts and refine your topic as you search. There are a variety of free tools you can use. Start with a basic topic or subject and think about various issues related to that topic. If you are researching a specific person, you might include branches for their childhood, education, career, etc. and then add off-shoots for accomplishments and challenges.