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.
Often, you'll discover the right level of focus as you begin your research. Encyclopedias and dictionaries can be a great place to start this research. Use these resources to get topic ideas or for background information.