Think about:
State your topic in one sentence. This helps you identify keywords/phrases that describe your topic.
How many pages do you need to fulfill your assignment? Knowing how many pages you need to write helps pinpoint just how much information you will need.
How many and what kind of sources are required? Knowing how many and what type of sources you need helps you choose a database and limit to the sources you need whether it be scholarly journals, books, newspapers, and/or statistics.