Pick a topic you enjoy! You want something that is broad enough that you can find information and yet narrow enough that you are not overwhelmed with sources.
Seek inspiration in the world around you!
Topics you find interesting are much easier to research and talk about. Also, learning about other perspectives on the issue enriches your understanding.
Turn your topic into a research question... or a series of related questions.
This will give you keywords to use in your research, defines the scope of your project, and gives you a research goal. Ask yourself: Does this article/book/etc. help answer my research question(s)?
For example: "fracking" becomes "What is the environmental impact of fracking in Pennsylvania?"
Research is also iterative and you may need to revise your questions and keywords several times during the process to get what you really want.
Find an expert. They lend you credibility.
Imagine that the authors of your sources are the people standing in the front of the room with you as you deliver your speech. Would you rather stand there alone or with a noted scientist?
Outside sources support and illustrate your point.
Sometimes a simple quote, phrase, statistic, or image can tell a story more simply and elegantly that you. Use that to your advantage! Just be sure to credit your source.