There are a plethora of strategies for brainstorming: free writing, concept mapping, etc. The links below highlight each strategy, so you can find the one that fits with your mode of thinking.
Whatever your strategy don't forget to review what your professor has asked for you to do, so you can make sure that your topic is appropriate for the assignment.
Assignments often are written with a subject in mind, but are often too broad to work as a single topic for your project. You still need to choose a unique aspect of that subject in which to specialize your research. To do this you may want to:
Below are some additional resources to get you started.