If your professor is allowing you to pick your own topic, think carefully. You want to make sure you pick something that has research available. Follow these steps:
If you're still uncertain, try checking out the Opposing Viewpoints database. This database collects information on controversial topics and is a great place to look for ideas that will have a lot of supporting material. You might also want to check the news for interesting stories that you'd like to research further.
Once you've selected a topic, it's time to move on to Step 2: Develop a Search Strategy.