Go from the general to the specific.
  • General: Animal behavior   Specific: Migration of birds

  • General: Education reform   Specific: Mandatory competency exams for teachers

  • General: AIDS    Specific: Current drug treatments for AIDS patients

But don't get too specific.

Top ten ways to train a dog to roll over.

Often your topic will evolve and get more specific as you do the research.

Similarly, you should start with general research sources and work toward ones with specific information.

For example, start with an encyclopedia, then go to a magazine article on a particular part of the topic.